Head and Neck Dissector

7/23/2019 Head and Neck Dissector

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Basic Head & Neck Instructions

Thirteen laboratory sessions are dedicated to dissection of the head and neck. There are probably as

many structures in the head and neck as in thorax and abdomen combined and they are all located

within a space about the same size as the pelvic girdle! As a dissection team you will want to plan your

work carefully and dissect the structures thoroughly. You can maximize your learning in the lab by taking turns

dissecting (usually only one or two people can work on the cadaver at the same time). Study the skull every

day and use pipe cleaners or thin wire to trace the routes of nerves and vessels through the foramina and across

the regions of the skull. Talk to each other (about head and neck!!) and draw charts and paths on the

blackboard.

In the first or second laboratory session(check your schedule) the ER residents from LIJ will demonstrate

the cricothyrotomy procedure. Please read the relevant case and related handouts prior to this lab and make

sure your cadaver is in the supine positionat the beginning of lab. If the procedure will be on the second lab

day you must not dissect the skin away from the midline of the neck during lab 1. Follow the directions

carefully for the dissection of the posterior triangle of the neck (Neck 1, Step 3).

The anterior, lateral and posterior aspects of the neck will be dissected during the first three laboratorysessions. You will begin on the posterior aspect with dissection of the suboccipital region. The cadaver must

be in the prone position. This dissection should be fairly fast because you have already dissected the deep

muscles of the neck (splenius and semispinalis). The suboccipital muscles and triangle lie just deep to the

semispinalis capitis muscles.

After dissecting the suboccipital triangles, turn the cadaver to the supine position for dissection of the posterior

triangle of the neck, also called the lateral cervical region. This region lies between the anterior margin of the

trapezius muscle and the posterior border of the sternocleidomastoid (SCM) muscle. The inferior boundary is

the clavicle. The posterior triangle/lateral cervical region contains many cutaneous nerves and portions of some

of the important fascias of the neck, including the investing fascia and prevertebral fascia. Deep to the

prevertebral fascia lie the scalene muscles and the roots of the brachial plexus.

The anterior triangle of the neck(between the SCM and the midline of the neck) contains several sets of

muscles involved in moving the hyoid bone and anterior cartilages of the neck during speaking and

swallowing. It also contains some essential neurovascular structures including the phrenic and vagus nerves

and the sympathetic chain and ganglia, the common carotid artery and its branches, and the internal jugular

vein and its tributaries.

Following dissection of the neck, one entire lab sessionis dedicated to study of the skull. This is a dry lab

held in the Belfer building. Two dissection teams will work with one instructor to identify and discuss the

details of the skull. You must bring your bone boxes and a text and atlas to this session.Advanced

preparation on your part will significantly enhance the value of the session.

Dissection of the head begins with the face. The muscles of facial expression and the motor and sensory

nerves of the face will be revealed. The pathways of the facial artery and vein will be traced and the superficial

structures of the orbit and eye will be explored.

Two lab sessions are devoted to dissection of the parotid regionon each side of the face. The parotid glands

are important salivary glands and running right through the middle of each gland are the facial branches of CN

VII, the external carotid artery and the retromandibular vein! Deep to these structures you will dissect the

temporal region including the temporomandibular joint. These dissections take you deep into the sides of the

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face and reveal the maxillary artery (a major artery of the face) and the mandibular division of CN V.

The study of thescalpbegins the preparation for removal of the calvarium(the top of the skull) and

subsequent removal of the brainfrom the cranium. The scalp is a very clinically important structure and each

one of you will undoubtedly have to suture a scalp wound during your training, so make the most of your

dissection of the scalp.

Special care must be taken when removing the brainbecause the brains from these cadavers will be storedand used in your Nervous System course. During the process of removing the brain the structures of the cranial

dura will also be studied. This very important tissue does more that provide protection for the brain. It forms

venous channels that drain blood and CSF from the head into the jugular system, and pathways for nerve

distribution. You will observe and learn the surface anatomy of the brain, the cranial nerves and the major

vascular structures (circle of Willis) of the brain.

Once the brain is removed, you will conduct a thorough dissection of the orbit and eyeusing the superior

approach through the anterior cranial fossa. This approach gives the best understanding of the eye and related

musculature, nerves, vessels and glands. A deep dissection of the eye from the anterior approach will complete

the study of the orbit and eye.

Toward the end of the work in head and neck, dissection teams will be asked to use one of two differentapproaches to dissection of the deeper structures of the head. It will be important for you to read the directions

for both of these dissections and consult with your instructors to determine which dissection your team will

prepare. Realize that you need to be able to identify structures revealed in both dissections.

The pharynx dissection and the oral/nasal cavity dissection are the two approaches that we will use to

explore the deeper structures of the head and neck. Be sure to follow the progress of your colleagues who

are conducting the dissection that you are not!

During the pharynx dissectionthe head will be separated from C1 and mobilized anteriorly to expose the

posterior aspect of the muscular pharynx. This dissection also reveals a number of cranial nerves and the

superior portions of the external and internal carotid arteries and the internal jugular vein. Following the study

and removal of the buccopharyngeal fascia the pharynx will be opened posteriorly and the posterior aspects of

the nasopharynx, oropharynx and laryngopharynx will be dissected. This unit ends with dissection of the larynx

including dissection of the vocal cords and the intrinsic muscles that move them, the epiglottis and regions of

the laryngeal airway (vestibule, ventricle, and infraglottis).

Those who do the dissection of the oral and nasal cavitieswill begin by bisecting the head along the

midsagittal plane. This procedure reveals the tripartite nasal septum, delicate curved conchae, and the intricate

collection of sinuses in the nasal cavities (frontal, maxillary, ethmoid, and sphenoid sinuses). The nasopharynx

houses the auditory tube and muscles that act on the soft palate. The oral cavity contains the teeth, tongue, and

the sublingual and submandibular salivary glands and is subdivided into regions the vestibule, floor and roof

which will be examined and dissected. The oropharynx contains the palatine tonsils and some of the many

muscles that attach to and move the tongue and pharynx. This dissection also permits exploration of the larynxthrough an anterior midline opening.

Finally, the middle and inner ear cavitieswill be dissected. This involves popping off the roof of the petrous

ridge with a chisel and hammer. The results are not 100% predictable but, if you follow the instructions

carefully, you will see many of the structures of the middle and inner ear including the tympanic membrane, the

ossicles, the semicircular canals, the cochlea, and the distribution of CNs VII and VIII.

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Read carefully, plan well, and work steadily and you will have a great dissection of the head and neck!

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Neck 1

General Overview

The neckis a major conduit between the head, trunk and upper limbs. It contains muscles, glands, major

arteries and veins (common, internal and external carotid arteries and various jugular veins), nerves,lymphatics, the trachea, larynx, esophagus and vertebrae. As in other regions of the body, understanding the

bony and cartilaginous framework of the neck provides important reference points and landmarks for learning

other structures and for palpation and dissection.

The structures in the neck are organized by the investing, prevertebral and pretracheal fasciaethat form

compartments and restrict or direct the flow of fluids, e.g. infectious material. One of these compartments can

transmit infectious material inferiorly into the thoracic cavity!! You must have a good understanding of the

fasciae of the neck.

The neck is subdivided (by anatomists) into the suboccipital regionand the anterior and posterior (lateral

cervical) triangles of the neck. The suboccipital regionlies on the posterior side of the neck between the

inferior aspect of the occipital bone (specifically the inferior nuchal lines) and C2 vertically, and as far lateralas the mastoid processes and transverse processes of C1. Dissection of the suboccipital region is often done

with the back unit. Therefore, in your texts you will find suboccipital information and review questions.

The anterior and posterior triangles of the neckare both accessible with the cadaver in the supine position.

(Therefore the posterior triangle of the neck is NOT on the posterior side of the body!) The posterior triangle

of the neck, also called the lateral cervical region, is the region posterior to the sternocleidomastoid muscle and

anterior to the anterior border of the upper trapezius muscle, extending from the mastoid process to the

clavicle. Structures in the posterior triangle include the platysma muscle, cutaneous nerves of the neck, the

external jugular vein, the splenius, levator scapulae and scalene muscles, roots and trunks of the brachial plexus

and some of the vasculature of the shoulder.

The anterior triangleis defined by the anterior border of the sternocleidomastoid muscle, the midline of the

neck and the mandible. The two anterior triangles share a common border at the midline of the neck. When

considered together they demarcate a large diamond shaped region across the anterior neck. The hyoid bone,

thyroid, cricoid and tracheal cartilages form the osteocartilagenous support for the muscles of the anterior

triangle. The structures of the anterior triangle of the neck include the platysma muscle, infra- and suprahyoid

muscles, the thyroid, parathyroid and submandibular glands, the carotid arteries and jugular veins, and several

important nerves including the phrenic and vagus nerves, the cervical sympathetic chain and ganglia, the ansa

cervicalis and CNs XI and XII.

The larynx, formed by the internal aspects of the tracheal and cricoid cartilages, will be studied later in the

head and neck unit in conjunction with the nasal and oral pharyngeal spaces.

Cricothyrotomy

This procedure will be demonstrated during the dissection of the neck by the Emergency Medicine residents

from LIJ Hospital. Do not dissect the skin over the midline of the neck until afterthe cricothyrotomy

demonstration!

The simplest and most rapid access to the airway inferior to the vocal cords may be created by making an

incision through the cricothyroid membraneand inserting a hollow tube. This technique, known as

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cricothyrotomy (or cricothyroidotomy), is an important lifesaving procedure that is often used prior to

tracheotomy(opening made in the trachea) in emergency situations. It is usually used when facial deformities

and profuse bleeding from the nose and mouth prevent oral endotracheal intubation.

Expose the neck region of the cadaver with the skin in place.1.

Palpate the thyroid cartilage and, inferior to it, the cricoid cartilage. Your fingers will move over the

cricothyroid membrane (ligament) as you move your hand inferiorly.

2.

After locating the cricothyroid membrane, incise it transversely. Your blade will cut through just twolayers, the skin and superficial fascia, before hitting the membrane.

3.

Once this membrane is penetrated, an emergency airway can be maintained with a hollow tube that is

inserted into the infraglottic cavity of the larynx.

4.

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Neck 1

Step 1

Surface Anatomy, Osteology and Fasciae of the Neck

Instructions

Before beginning dissection, study and palpate the surface anatomy of the neck.Pay close attention to

important clinical landmarks such as the external occipital protuberance, mastoid processes and spinous

processes of the vertebraeposteriorly and the laryngeal prominence, jugular notch and claviclesanteriorly

(refer to your atlas for an image). With deep palpation of the lateral side of the neck you can feel the solidness

of the tips of the transverse processes of the vertebraeeven though you can't feel a lot of detail. What is their

A/P position relative to the tip of the mastoid process? What is their A/P position relative to the vertebral

spinous processes and the anterior border of the neck? Be sure to practice these palpations on yourself or a

classmate. The neck is a region that is frequently palpated during the physical exam.

Surface anatomy of the anterolateral neck

Embedded in the subcutaneous tissue (hypodermis) of the anterolateral neck is the platysma muscle(refer to

your atlas for an image). This thin muscle tightens the skin over the neck and may be observed clearly when a

person makes an exaggerated grimace.

The sternocleidomastoid muscle(SCM) is a key landmark on the anterolateral neck (refer to your atlas for an

image). It separates the anterior and posterior triangles from each other. The SCM can be palpated as it passessuperolaterally from the manubrium (sternal head) and medial clavicle (clavicular head) to the mastoid process

of the skull. Watch the action of this muscle as you turn your head to the right or left. Put your hand against the

right side of your face and give resistance as you turn your head to the right. Which SCM muscle stands out

with this resistance? What does that mean?

Thejugular notch of the manubrium is located between the sternal heads of the SCM. Above this notch, in the

suprasternal space, you can palpate several of the proximal tracheal rings. Thejugular venous archlies

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anterior to the trachea in this region but is not normally palpable. Between the sternal and clavicular heads of

the SCM, just superior and lateral to the sternal extremity of the clavicle, there is a depression that contains the

inferior end of the internal jugular vein(IJV) (refer to your atlas for an image). This site is often used to

access the IJV during central line placement or catheterization of the heart.

Palpate the soft tissues anterior to the SCMand just inferior to the angle of the mandible . You should be

able to feel the carotid pulsethere and, if you have a cold or sore throat, you may be able to palpate some of

the numerous superficial lymph nodesof the neck. Continue palpating anteriorly, inferior to the mandible, andidentify the midline laryngeal prominence (Adams apple).It is a protrusion of the thyroid cartilage (refer to

your atlas for an image) and is generally larger and more prominent in men. The hyoid bonelies superior to the

thyroid cartilage and the cricoid cartilage lies inferior to it. You can access the airway by puncturing the

cricothyroid membrane (ligament) that stretches between the thyroid and cricoid cartilages. The ER residents

will demonstrate this procedure during one of your lab session.

Osteology of the Neck

The skeleton of the neck includes the cervical vertebrae as well as the hyoid bone and several cartilages that lie

anterior to the vertebral column (refer to your atlas for an image). Specifically there are:

seven cervical vertebraea U-shaped hyoid bone

several midline cartilaginous structures

thyroid and cricoid cartilages that, with associated smaller cartilages, constitute the larynx

6-8 tracheal rings

The manubrium of the sternum and the clavicles define the inferolateral aspect of the anterior neck. They

provide landmarks for palpation and identification of deeper structures, as well as attachment sites for muscles

associated with the neck. The manubrium was discussed in detail in the thorax unit. The clavicles are discussed

in detail in the upper limb unit.

Cervical Vertebrae

Of the seven cervical vertebrae, the atlas and the axis are unique while C3-C7 share many common

characteristics. Refer to an atlas and to the skeleton to review the detailed structure of the cervical vertebrae.

C1 and C2 are atypical vertebrae. Learn their unique characteristics and be able to identify these individual

vertebrae.

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Atlas (C1) a unique cervical vertebrae Axis (C2) a unique cervical vertebrae

Atlas (C1):

ring-likebone

lacks both spinous process and vertebral body

consists of two lateral massesconnected by anterior and posterior arches

anterior and posterior tuberclesare located centrally on each arch

the posterior arch has groove for vertebral arteryon its superior surface

the large horizontal superior articular facetslie directly medial to the transverse processes and

articulate with the occipital condylesof the skull

inferiorly C1 articulates with C2 via the densand two lateral inferior articular facets

Axis (C2):

has a body with the dens(odontoid process) projecting superiorly from it

the densarticulates with the anterior arch of C1 (synovial pivot joint)

has a spinous processthat is, usually bifid

the superior articular facetslie anteromedial to the transverse processes and articulate with the C1

inferior articular facets v ia gliding synovial joints

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Typical cervical vertebrae (C3-C7):

Typical cervical vertebrae 7th cervical vertebrae (vertebra prominens)

large triangular vertebral foramen

vertebral bodywider from side to side than anteroposteriorly with a concave superior surface andconvex inferior surface

transverse processes with a foramen (transverse foramen) to accommodate the vertebral artery and

vein

anterior and posterior tubercleslateral to each transverse foramen

obliquely orientedarticular facets that lie posteriorto the transverse processes

short bifid spinous process(except for C7)

Notice that the bodies of the cervical vertebrae have superolateral ridges called uncinate processes. Also, each

articular processof a typical cervical vertebra forms a bulge posterior to the transverse process. On C6 the

large anterior tubercle of the transverse process is called the carotid tuberclebecause the common carotid

artery can be compressed against it and the vertebral body to control bleeding. Finally, C7, the vertebra

prominens,has a very long spinous process that is not bifid.

Hyoid Bone

The U-shaped hyoid bonelies in the anterior part of the neck at the level of the C3 vertebra (refer to your atla for an

image). It is suspended by horizontally-oriented muscles attached to the mandible and styloid processes

and vertically oriented muscles attached to the thyroid cartilage, manubrium and scapulae inferiorly. The hyoid

bone consists of a bodyand right and left greater and lesser horns.

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Hyoid bone Hyoid bone and cartilages of the neck

Cartilages of the Anterior Neck

Two large and distinct cartilages, the thyroid and cricoid cartilages, are suspended from the hyoid bone in the

central portion of the anterior neck (refer to your atlas for an image). The thyroid cartilageis the largest and

most superior of the two. It is a shield-shaped structure formed from two relatively flat plates of cartilage

(lamina) that fuse in the midline and create the laryngeal prominence. The thyroid cartilagesare open

posteriorly. Superior and inferior hornsproject from the posterior aspect of each lamina and provideattachment sites for the thyrohyoid membrane superiorly and the cricothyroid joint inferiorly.

The cricoid cartilageis shaped like a signet ring with its broad laminafacing posteriorly and its narrow arch

(band) facing anteriorly (refer to your atlas for an image). The cricoid cartilage is the only complete ring of

cartilage to encircle the airway! It is very strong. It is attached to the thyroid cartilage by the median

cricothyroid membrane(ligament) which is easily incised to access the airway in an emergency. Inferiorly,

the cricoid cartilage attaches to the first tracheal ring by the cricotracheal ligament.

More details of this region will be covered in the study of the larynx.

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Fasciae of the Neck

The fascial layers of the neck

Superficial and deep cervical fasciaesubdivide the neck into compartments that separate structures and direct

the flow of fluid (e.g. infectious materials) in the neck. It is very important to know the distribution of thesefasciae and the structures within the compartments they define (refer to your atlas for an image).

Superficial Cervical Fascia:

The superficial cervical fasciais a loose fatty layer of subcutaneous tissue that lies between the dermis of the

skin and the investing layer of the deep cervical fascia. The thickness of the superficial cervical fascia varies

among people. It contains cutaneous nerves, blood vessels and lymphatics as well as the platysma muscle - a

thin broad muscle that tightens the skin of the anterolateral neck.

Deep Cervical Fascia (three layers):

The deep cervical fasciaof the neck consists of three layers of membranous fascia that form compartments

and separate muscle layers and neurovascular structures. The investing layer (red) is the most superficial of

the deep cervical fascias. It surrounds the entire neck just deep to the superficial cervical fascia. Posteriorly it

attaches to the superior nuchal line, ligamentum nuchae and spinous processes of the cervical vertebrae.

Anterolaterally it attaches to the mastoid processes, the zygomatic arches (of the face), and the mandible and

hyoid bones. It encloses the SCM and trapezius musclesby splitting into superficial and deep layers around

these muscles. It also encloses the submandibular and parotid glands.

The pretracheal layer(purpleand blue) is found in the anterior neck. The muscular portion of pretracheal

fascia (purple) is a thin layer that encloses the infrahyoid muscles. The visceral portion (blue) is more distinct

and encloses the thyroid gland, trachea and esophagus. Superiorly, it attaches to the hyoid boneand forms a

pulley that anchors the intertendon of the digastric muscle. Inferiorly it is continuous with the fibrous

pericardium. Laterally it blends with the carotid sheath. Posteriorly it is continuous with the

buccopharyngeal fasciaof the pharynx.

The prevertebral layer (orange) ensheaths the vertebral column and its manyassociated muscles:

anteriorly the longus colli and capitis; posteriorly the deep (intrinsic) muscles of the back (splenius,

longissimus, semispinalis etc.); and laterally the scalene muscles. Superiorly it is attached to the cranial base.

Inferiorly it blends with the anterior longitudinaland supraspinous ligaments. At the base of the neck (near

the midpoint of the clavicles) the prevertebral fascia is drawn out laterally as the axillary sheathby the nerve

roots of C5-T1 that form the brachial plexus. Posteriorly, the prevertebral fascia attaches to the spinous

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processes of cervical vertebrae. Anteriorly, some authors describe an additional layer, the alar fascia, that lies

between the pretracheal and prevertebral fasciae subdividing the retropharyngeal space. The alar fascia attaches

to the carotid sheaths on each side.

The carotid sheathis a condensation of fascia that encloses the common and internal carotid arteries, the

internal jugular vein, the vagus nerveand some deep cervical lymph nodes(refer to your atlas for an

image). It extends from the base of the skull to the root of the neck and receives fascial contributions from all

three layersof deep cervical fascia.

Cricothyrotomy

This procedure will be demonstrated during one of the first lab sessions for dissection of the neck. The cadaver

must be in the supine position. Do not dissect the skin over the midline of the neck until afterthe

cricothyrotomy demonstration!

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Neck 1

Step 2

Suboccipital Triangle of the Neck

Dissection Instructions

Position of cadaver = prone

With the cadaver in the prone position,review your previous dissection of the posterior cervical region.

Identify the semispinalis capitis musclesand the greater occipital nerve (dorsal ramus of C2) (refer to your

atlas for an image). This nerve, which pierces the superior aspect of the semispinalis capitis, is quite thick and

contains only cutaneous axons to the posterior scalp. If you don't see it right away, you can continue your work

and look for it as you go.

Palpate the external occipital protuberance, spinous process of C2, mastoid processes and the transverse

processes of C1 and C2on your cadaver. Also, find these bony landmarks on the skeleton. Note the

relationship of the mastoid process and the C1 transverse process. Also note the difference in length between

the C1 and C2 transverse processes.

Semispinalis capitis Semispinalis capitis reflected

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The left and right suboccipital triangleslie deep to the semispinalis capitis muscles (refer to your atlas for an

image). The borders of each triangle are defined by three small muscles: the rectus capitis posterior major

and the superior and inferior oblique muscles of the head (obliquus capitis superior and inferior).A

fourth muscle, the rectus capitis posterior minor, lies medial and deep to the rectus capitis major muscle and

does not form a border of the triangle.

Carefully cut the superior attachment of semispinalis capitisclose to the skull. Semispinalis capitis is a very

thick muscle (about 1cm) and the suboccipital muscles lie just deep to it so take care when cutting!! Look forthe intermuscular fascial plane. As you are cutting look again for the greater occipital nerve. Take care not to

damage it as you reflect semispinalis capitis. Free the right and left semispinalis capitis muscles from the skull

and reflect them inferolaterally.

Suboccipital triangle with suboccipital nerve and greater occipital nerve

(RCPM - rectus capitis major muscle; SO - superior oblique muscle; IO - inferior oblique muscle)

Gently clean away the fat and areolar tissue deep to semispinalis and expose the rectus capitis posterior

major and minor muscles. The rectus major is a relatively large fan-shaped muscle. It attaches inferiorly to

the C2 spinous processand forms the medial border of the suboccipital triangle. Rectus major is usually

very distinct, but you can make it stand out more by rotating the head to the opposite side of the muscle you are

working on. With the head in this position, clean and define the borders of rectus major. Look for the inferior

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oblique musclethat also attaches to the C2 spinous process. What is its orientation? What does it attach to

laterally?.

Medial and deep to rectus major is the rectus capitis posterior minor. This small fan-shaped muscle attaches

to the medial aspect of the inferior nuchal line superiorly and the posterior tubercle of C1inferiorly. It lies

immediately adjacent to the midline of the neck and does not form a border of the suboccipital triangle.

The inferior oblique muscleis oriented horizontally with attachments to the tips of the C2 spinous processand the C1 transverse process.It defines the inferior boundary of the suboccipital triangle. Clean the

muscle all the way to its lateral attachment. Based on its fiber direction, what is its action?

At the transverse process of C1find the inferior attachment of the superior oblique muscle. Its superior

attachment is to the lateral aspect of the occipital bone between the superior and inferior nuchal lines. The

superior oblique muscle forms the lateral border of the suboccipital triangle. Clean this muscle and now you

should clearly see the suboccipital triangle.

Emerging from the center of the suboccipital triangle are branches of the suboccipital nerve(dorsal ramus of

C1) that innervate the 4 suboccipital muscles (refer to your atlas for an image). Gently clean the fascia out of

the center of the triangular space and find the suboccipital nerve and its branches. Demonstrate the motor

points (point where the nerve enters the muscle) of the branches.

On one side only (the side with the least beautiful suboccipital muscles), reflect the suboccipital muscles and

identify the posterior arch and transverse process of C1 and the transverse and spinous processes of C2. Look

for the vertebral arterypassing vertically through the transverse foramina of C1 and C2 (refer to your atlas for

an image). Follow it as it ascends and turns medially to travel in a groove on the superior surface of the C1

posterior arch just posterior to the superior articular process. Follow it as it passes through the atlantooccipital

membrane stretched between the posterior arch of the atlas and the posterior margin of the foramen magnum.

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Neck 1

Step 3

Posterior Triangle of the Neck - Suprficial Dissection


Position of the cadaver = supine.

The anterolateral neck is subdivided by the sternocleidomastoid muscle (SCM) into anterior and posterior

triangles (refer to your atlas for an image). The posterior triangle, also called the lateral cervical region, is

further subdivided into occipitaland supraclavicular(subclavian, omoclavicular) trianglesby the inferior

belly of the omohyoid muscle. In addition to the omohyoid muscle, the posterior triangle of the neck contains

many cutaneous nerves, a motor nerve, the(spinal) accessory nerve (CN XI), the inferior portion of the

external jugular veinand the transverse cervicaland suprascapular arteries and veins. Study the drawings

of the cervical triangles in your altas and note the borders and subdivisions of the posterior triangle of the

neck. The floor of the posterior triangle contains portions of the splenius capitis, levator scapulae and thescalene muscles.

Boundaries of the anterior and posterior triangles

of the neck

Subdivisions of the anterior and posterior triangles

of the neck

Borders of the Posterior Triangle of the Neck:

Anterior:posterior border of sternocleidomastoid muscle (SCM)

Posterior:anterior border of trapezius muscle

Inferior:middle third of the clavicle

The posterior triangle has a fascial roofcomposed of the investing layer of deep cervical fasciaand a fascial

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floorformed from prevertebral fascia(refer to your atlas for an image). The investing fascia splits to envelop

the adjacent trapezius and sternocleidomastoid muscles and is pierced by the external jugular veinand

cutaneous nervesof the neck. The prevertebral fascia which forms the floor of the triangle, covers the splenius

capitis, levator scapulae and scalene musclesand the roots of the brachial plexus.

In its inferior aspect, the posterior triangle of the neck is divided by the inferior belly of the omohyoid muscle

into a large occipital trianglesuperior to the omohyoid and a small supraclavicular (subclavian,

omoclavicular)triangle inferior to it. The occipital triangle contains the occipital arteryat its apex and severalnerves including the accessory nerve (CN XI). The supraclavicular triangle contains the external jugular

veinand the suprascapular artery and vein(refer to your atlas for an image).

Anterior neck skin incisions Platysma

YOU MUST DISSECT BOTH RIGHT AND LEFT POSTERIOR TRIANGLES OF THE NECK!!

Because you have already dissected the thorax, an incision has been made along the clavicle from its medial

end to a point beyond the acromion process. Beginning at the inferolateral border of the cut skin, near the

acromion process, use a forceps and small scissors to lift and separate the skin along its fascial plane. The skin

is very thin over the neck. The platysma muscle, cutaneous cervical nerves and the external jugular vein

lie just deep to it. Take great care in reflecting the skin!

TIP:The skin in this area is extremely thin. Cut carefully!

Continue to reflect and remove the skin over the posterior triangle of the neck from the inferolateral

border of the clavicle to the anterior border of the SCM. Clean as far superiorly as the auricle of the ear.

Identify the platysma muscle (refer to your atlas for an image). Its fibers arise in the fascia overlying the

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clavicle and pectoralis major muscle and sweep superomedially over the mandible to interdigitate with the

muscles of the lower face. (You will see much more of platysma after removing the skin from the anterior

triangle of the neck in the next unit.) The platysma is innervated by CN VII, the facial nerve. This nerve

innervates all of the muscles of facial expression and, even though platysma is located on the neck, it is

activated during some of the facial expressions that we make (e.g. grimace). The cervical branch of CN VII

will be dissected with the face.

Carefully reflect platysma superomedially. Keep it intact so you can see the entire muscle after removing theskin from the anterior triangle. Look for the external jugular vein(EJV) as it crosses the midpoint of the SCM

(refer to your atlas for an image). It descends superficial (external) to the SCM draining venous blood from the

scalp and face. Near the clavicle the EJV pierces the investing layer of deep cervical fasciaand terminates in

the subclavian vein just posterior to the clavicle.

TIP:If the EJV is severed its lumen is held open by the tough investing fasica and, due to

negative intrathoracic pressure, air will be sucked into the vein creating an air embolism. The

best way to prevent this is to apply firm pressure to the severed jugular vein until it is sutured to

stop the bleeding and entry of air.

In the same plane as the EJV, at the point where it crosses the posterior border of the SCM, look for thecutaneous nerves of the neck (cervical plexus) and the accessory nerve, a motor nerve (refer to your atlas

for an image). This area is often called the nerve point of the neck (punctum nervosa) because of the large

number of nerves that pass through the small region.

Posterior triangle of the left neckCutaneous nerves and superficial vessels of the

right neck

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Carefully pick away the investing fascia(roof) over the posterior triangle and identify and clean the following

nerves (refer to your atlas for an image):

great auricular nerve (C2, C3):travels parallel to the EJV from the punctum nervosa to the auricle of

the ear which it innervates, also provides sensory innervation to the parotid gland (source of pain with

mumps)

transverse cervical nerve (C2, C3):runs transversely across the middle of the sternocleidomastoid

muscle to supply the skin of the anterior triangle of the necklesseroccipital nerve (C2): a small diameter nerve that runs superoposteriorly, parallel to the posterior

border of the SCM, to supply the scalp over the occipital bone posterior to the auricle of the ear

supraclavicular nerves (C3, C4):pierce the investing fascia in the inferior part of the neck and supply

the skin covering the clavicle. There are three branches (groups): medial, intermediate and lateral

supraclavicular nerves

accessory nerve (CN XI):exits the jugular foramen (not visible on the cadaver at this time but find it

on the skeleton) and travels deep to the SCM (which it innervates) until it emerges in the superior part of

the punctum nervosa. CN XI runs inferolaterally across the posterior triangle of the neck and enters the

deep surface of the trapezius muscle about 5 cm superior to the clavicle. CN XI is a somatic motor

nerve!!

In the inferior portion of the posterior triangle find the inferior belly of the omohyoid muscle (refer to your

atlas for an image). This muscle originates on the scapula (superior border just medial to the suprascapular

notch), passes through a sling of fascia on the deep surface of the SCM and turns superiorly to insert on the

hyoid bone. It is one of the infrahyoid muscles and will be studied with the anterior triangle of the neck. Clean

and preserve it in situ.

Look for the occipital artery in the apex of the posterior triangleof the neck at the point where the SCM

meets the trapezius muscle superiorly (refer to your atlas for an image). It is a branch of the external carotid

artery and supplies the scalp over the occipital bone.

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Neck 1

Step 4

Posterior Triangle of the Neck Deep Dissection


Carefully remove the prevertebral fascia (floor of the posterior triangle of the neck) (refer to your atlas for an

image). Do not to destroy the nerves, muscles and vessels you have already found. As you remove the

prevertebral fascia identify the splenius capitis, levator scapulae and scalene muscleslying deep to it.

Splenius and levator lie in the superior part of the occipital triangle deep to the prevertebral fascia. Verify that

you have correctly identified these muscles by checking your earlier dissection of these muscles in the back

unit.

Deep posterior triangle

(EJV - external jugular vein)

TIP:It is a good idea to review a cross-sectional drawing of the fascias of the neck and get a

clear idea of where the prevertebral fascia that you are removing lies!

The three scalene musclesform the inferior muscular mass deep to the floor of the posterior triangle (refer to

your atlas for an image). Between the anterior and middle scalenes lie the roots and trunks of thebrachial

plexus. In the anterior inferior part of the posterior triangle, identify and clean the omohyoid muscle. Only the

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inferior belly of omohyoid is visible at this time. It subdivides the posterior triangle into the large occipital and

small supraclavicular (subclavian) triangles (refer to your atlas for an image). The superior belly of omohyoid

will be seen later.

On one side of the body, free the distal ends of the supraclavicular nervesand move them laterally in

preparation for reflecting the clavicular head of the SCM. Clean the area around the inferior aspect of the

SCM and place the handle of a scalpel just deep to the muscle to protect the underlying structures. Cut the

clavicular head close to the bone (what bone?) and reflect it medially.

Left interscalene triangle

(IJV - internal jugular vein)Left interscalene triangle

In order to have better access to the deep posterior triangle, resect a small part of the clavicle on the same side

of the body that you reflected the clavicular head of SCM. Use a small hand saw to cut the claviclejust medial

tothe attachment of the trapezius muscle. Take care -do not cut the accessory nerve! Now cut through the

clavicle at the attachment site of the now reflected clavicular headof the SCM.

Roll the cut portion of the clavicle forward and sever the attachment of the subclavius musclefrom its inferior

surface (refer to your atlasfor an image). Remove the now free section of clavicle. Examine the medial attachment o

subclavius muscle to the first rib and costal cartilage. Subclavius retracts and depresses the clavicle and resists

forces that pull the clavicle forward. The clavicle will be studied with upper extremity.

Examine the anterior scalene muscle and clean away any loose fascia from the region. The anterior scalene

muscle attaches superiorly to the transverse processes of C4-C6 and inferiorly to the first rib (refer to your atlas

for an image). With the section of clavicle removed you should be able to palpate its attachment on rib 1. On its

anterior surface the anterior scalene muscleis crossed transversely by the transverse cervical and

suprascapular arteries (and veins) and vertically by the phrenic nerve. Verify your identification of the

phrenic nerve by tugging on its intrathoracic segment. The cervical segment should move.

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The middle scalene muscle lies posterior to the anterior scalene and attaches to the cervical transverse

processes of C1-C6 and the first rib posterior to the anterior scalene. The anterior and middle scalene

muscles, and the related segment of the first rib, define the interscalene trianglewhich transmits the

subclavian arteryand vertically by the and roots of the brachial plexus (refer to your atlas for an image).

The posterior scalene muscleis rather difficult to see with the cadaver supine because it lies posterior to the

large middle scalene muscle. It attaches to C4-C6 transverse processes and the second rib. Make a note to look

for it next time you turn the cadaver to the prone position.

Clean the newly visible part of the omohyoid muscle(refer to your atlas for an image). What is the origin of

omohyoid?

TIP: "Omo-"refers to the scapula

Trace the external jugular veinto the subclavian vein (refer to your atlas for an image). Clean the loose

fascia and lymph nodes from the region posterior to the clavicle and verify that the subclavian vein lies anterior

to the anterior scalene muscle. Find the following blood vessels:

Suprascapular artery and vein (refer to your atlas for an image): run parallel and posterior to the clavicle,

superficial to the floor of the posterior triangle but deep to the inferior belly of the omohyoid. Ultimately they

pass through the suprascapular notch of the scapula to supply the supra- and infraspinatus muscles. If the upper

trapezius muscle is reflected you will be able to follow the suprascapular vessels over to the scapula. The artery

is a branch of the thyrocervical trunk. The vein empties into either the external jugular or subclavian vein.

Transverse cervical arteryand vein(refer to your atlas for an image): branch of the thyrocervical trunk that runs

posteriorly across the shoulder superficial to the floor of the posterior triangle but deep to the inferior belly of

the omohyoid. It supplies the trapezius, levator scapulae, and rhomboid muscles.

Trace the transverse cervical and suprascapular arteries back to their origins from the thyrocervical trunk

(variations occur in the origins of these vessels) (refer to your atlas for an image). If doing this dissection inyour cadaver is very difficult right now, wait until you reflect the rest of the SCM and then find the

thyrocervical trunk.

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Neck 2

General Overview

The anterior triangle of the neckis a fairly large region and contains many significant structures including the

carotid artery and its branches, the internal jugular vein and its tributaries, cranial nerves X, XI and XII, theinfrahyoid and suprahyoid muscles involved in swallowing, the thyroid, parathyroid and submandibular glands,

and the midline hyoid bone and thyroid, cricoid and tracheal cartilages. The boundaries of the anterior triangle

are:

Superior border (base): inferior border of the mandible

Posterior border: anterior border of the sternocleidomastoid muscle

Anterior border: midline of the neck

Roof: investing layer of deep cervical fascia covered by superficial (subcutaneous) fascia with the

platysma muscle

Floor: pharynx, larynx and thyroid gland

Apex: jugular notch of the manubrium

Boundaries of the anterior and posterior triangles

of the neck

Subdivisions of the of the anterior and posterior

triangles of the neck

The anterior triangle of the neck is divided into suprahyoid and infrahyoid regionsand each of these issubdivided into two smaller triangles the muscular and carotid trianglesand the submandibular and

submental trianglesrespectively. The first dissections will be of the muscular and carotid triangles in the

infrahyoid region.

The muscular trianglecontains the infrahyoid (strap)muscles. These four small muscles attach to the hyoid

bone or thyroid cartilage and mediate movements of the larynx during swallowing and speaking. Reflection of

the infrahyoid muscles will reveal the cartilages of the neckand the thyroid gland.

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In the carotid trianglethe common carotid arterydivides into the internal and external carotids. You will

clean and follow branches of the external carotid to their various destinations in the neck. The large

hypoglossal nerve (CN XII) traverses the superior aspect of the carotid triangle and carries with it the C1 root

of the ansa cervicalis.

In the suprahyoid region the submandibular trianglecontains the submandibular gland, the facial vessels

and CN XII.

The submental triangleis a midline region bounded by the left and right anterior bellies of the digastric

muscles. It contains the mylohyoid muscle.

The root of the neckis the region adjacent to the superior thoracic aperture. It lies posterior to the manubrium

and medial extremity of the clavicle, between the right and left first ribs, and anterior to the body of T1. The

root of the neck contains the structures that pass through the superior aperture of the thorax. You have seen

some of these structures in earlier dissections.

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Neck 2

Step 1

Review Bones, Cartilages, Fascias and Structures of the Anterior Triangleof the Neck

Instructions

Study a diagram of a cross-sectional view of the neck(refer to your atlas for an image). Note the relative

positions ofvessels, nerves, muscles, viscera and the bony and cartilaginous structuresof the anterior region

of the neck. Identify the related fascial layersincluding the investing fascia that envelops the SCM muscles,

both the muscular and visceral portions of the pretracheal fascia, and the anterior part of the prevertebral

fascia. Review the carotid sheath. What structures do you expect to find enclosed by the carotid sheath? What

fascial layers contribute to the carotid sheath?

The viscera of the anterior cervical regioninclude the superior portions of the digestive and respiratory

systems (pharynx, esophagus, larynx and trachea) as well as the thyroid, parathyroid and submandibularglands.

Bony and cartilaginous structures of the anterior triangle of the neck(refer to your atlas for an image:

Hyoid bone and cartilages of the anterior neck

Hyoid bone:lies at the angle between the floor of the mouth and superior end of the neck. Identify the

body, greater horn and lesser horn of the hyoid in a bony specimen and understand the orientation of the

bone in the neck. The hyoid bone is the only bone in the body with no bony articulations.

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Thyroid cartilage:largest cartilage of the larynx, formed of two flat plates that meet in the midline and

form the laryngeal prominence (Adam's apple) anterosuperiorly. Posteriorlythe thyroid cartilage is open.Thyrohyoid membrane:joins the thyroid cartilage and hyoid bone.

Cricoid cartilage: lies at the level of C6, inferior to the thyroid cartilage, superior to the 1st tracheal

ring. It is a strong, complete ring of cartilage.

Cricothyroid membrane(ligament): joins the cricoid and thyroid cartilages. It is incised during the

cricothyrotomy procedure.

Fasciae related to the anterior triangles of the neck:

Fasciae of the neck in cross section

Prevertebral layer of deep cervical fascia(orange): is cylindrical and encloses the vertebral column

and associated muscles. The part related to the anterior cervical region covers the longus colli and longus

capitis muscles and the anterior scalenes. Prevertebral fascia contributes to the carotid sheath.Pretracheal layer of deep cervical fascia(blueandpurple): invests the infrahyoid muscles and the

larynx, trachea and thyroid glands. It contributes to the carotid sheath.Investing layer of deep cervical fascia(red): surrounds all of the structures of the neck deep to the

subcutaneous (superficial) fascia. It divides to enclose the sternocleidomastoid and trapezius muscles.

Viscera of the anterior triangle of the neck(refer to your atlas for an image):

Thyroid and parathyroid glands- lie in the inferior part of the infrahyoid region against the trachea

and larynx, these endocrine organs have a rich blood supply

Submandibular gland -a suprahyoid salivary gland

Pharynx and esophagus -proximal part of the digestive system (will be dissected later)

Larynx and trachea -proximal part of the respiratory system (will be dissected later)

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Neck 2

Step 2

Muscular Triangle of the Neck


The skin, superficial fascia and platysma muscle must be reflectedfrom the anterior cervical region (refer

to your atlas for an image). Reflect (or remove) the skin beginning at its clavicular edge and carry it over the

superior border of the mandible. Remember that the skin is very thin and the platysma lies just deep to it. If you

preserved the portion of the platysma that extends into the posterior triangle, you can use it as a guide for how

deep to cut when removing the skin and superficial fascia over the anterior triangle.

After removing the skin, scrape away the fatty layer of superficial fasciacovering platysma until you can

see the entire muscle (refer to your atlas for an image). Note that it extends over the superior margin of the

mandible and interdigitates with some of the muscles of facial expression. Clean the anterior surface of the

platysma as far superior as the superior border of the mandible.Then reflect platysma superiorlystartingat its inferior margin. It is ok to leave a thin layer of superficial fascia on the deep surface of platysma to help

hold it together. At the angle of the neck, where the mandible and floor of the mouth meet the vertical part of

the neck, reflecting the platysma can become a little difficult because the contours of the deep structures are not

smooth and predictable like the vertical neck. Just use the muscle fibers as your guide and continue to

expose the deep surface of platysmauntil you can reflect the muscle all the way over the margin of the

mandible. Look along the margin of the mandible for the facial artery and vein (refer to your atlas for an

image). They lie in a shallow depression on the inferior border of the mandible about 1/3 of its length from the

angle. Preserve the facial vessels.

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PlatysmaMuscular triangle

(SCM - sternocleidomastoid muscle)

TIP:The facial artery is easy to palpate along the mandible of a living person and has a very

discernible pulse. It crosses the inferior margin of the mandible about 4 cm anterior to the

angle. Remember do not use your thumb when feeling for a pulse!!

Look for the transverse cervical nervecrossing the SCM at its midpoint, and look for tributaries of the jugularvenous system (refer to your atlas for an image). The anterior jugular veinruns parallel to the midline of the

neck. This vertical vein may be paired or singular. Communicating jugular veinsmay run obliquely parallel

to the anterior border of the SCM and unite the facial or retromandibular veins with the anterior jugular veins

inferiorly (refer to your atlas for an image).

The muscular triangle is a subdivision of the anterior triangle of the neck. It is a part of the infrahyoid

region and is bounded by the superior belly of the omohyoid muscle, the anterior border of the SCM

muscle and the midline of the neck (refer to your atlas for an image). The hyoid bone defines its superior

extent and thejugular notchdefines its inferior extent. The muscular triangle contains the four infrahyoid

musclesand the thyroid and parathyroid glands.

The infrahyoid musclesattach to the hyoid bone or thyroid cartilage superiorly and the manubrium or scapulainferiorly (refer to your atlas for an image). They are involved in stabilizing or moving the hyoid bone and

thyroid cartilage during swallowing and vocalization. The muscles are arranged in two layers with two

muscles superficial and two deep. Three of the four infrahyoid muscles are innervated by branches from C1-C3

that travel in a special plexus - the ansa cervicalis (refer to your atlas for an image). One muscle, the

thyrohyoid, is innervated by a branch of C1 that takes a different path. These nerves will be dissected with the

carotid triangle because of their pathway in the neck.

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Clean the anterior surface of the infrahyoid musclesand identify the omohyoid (superior belly) and

sternohyoid muscle.Which is the most lateral?Both of these muscles attach to the hyoid bone superiorly.

The sternohyoidis most medial at the hyoid and attaches to the deep surface of the manubrium inferiorly. With

contraction of this muscle, what direction will the hyoid bone move?

The omohyoid attaches to the hyoid bone lateral to sternohyoid. It descends inferolaterally but before reaching

the manubrium it angles sharply laterally and makes its way to the superior border of the scapula. There it

attaches just medial to the suprascapular notch (refer to your atlas for an image). At the midpoint of the muscle,

where its angulation is greatest (at the level of the cricoid cartilage), muscle tissue is replaced by an

intermediate tendon. A fascial sling,originating from the clavicle, wraps around the tendon and anchors it

in place. The intermediate tendon provides both the inferior attachment of the superior belly of omohyoidand

the superior attachment of the inferior belly of omohyoid. The inferior belly continues from the tendon

across the posterior triangle of the neck (subdividing it), to the scapula.

Superficial infrahyoid musclesDeep infrahyoid muscles

(OH - omohyoid muscle)

In order to see the full extent of the omohyoidmuscles and for better access to the carotid triangle, reflect

both SCMs by cutting their inferior attachments from the manubrium and clavicle. Do this with great care as

there are many important structures that lie deep to the SCM. You may want to put the handle of a scalpel

posterior to the muscle while you cut. Cut close to the bones. Carefully reflect SCM and clean the loose fascia

away until you can see the full extent of omohyoid. Look for the fascial sling. Keep track of the cutaneous

nerves that are related to the SCM at the punctum nervosa. You dissected them with the posterior triangle.

On one side of the body, reflect sternohyoid and omohyoidfrom their superior attachments in order to see the

deep infrahyoid muscles. Cut both muscles about 1 cm inferior to the hyoid bone and reflect them inferiorly.

Clean and identify the short broad thyrohyoid muscle(refer to your atlas for an image). Note its inferior

attachment to the oblique line of the thyroid cartilage. Thyrohyoid receives innervation from C1 via the

hypoglossal nerve. What are the possible actions of the thyrohyoid muscle?

The sternothyroid muscle attaches to the thyroid cartilage just inferior to the thyrohyoid muscle. From the

inferior attachment of the thyrohyoid follow the sternothyroidinferiorly to the deep surface of the manubrium.

This muscle widens inferiorly. It receives innervation from the ansa cervicalis. When it contracts it depresses

the thyroid cartilage.

Now, cut the sternothyroidmuscle close to its attachment on the thyroid cartilage and reflect it inferiorly to

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expose the thyroid gland(refer to your atlas for an image). Find the very distinct superior thyroid artery

going to the superior pole of the gland. Palpate the isthmus of the thyroid gland- the part that connects right

and left lobes across the midline of the neck (refer to your atlas for an image). A more detailed dissection of the

thyroid and parathyroid glands will be conducted later. Preserve the neurovascular structures in this region.

Thyroid gland

Inspect the midline of the neck between the infrahyoid muscles. With one sternohyoid muscle reflected you

should be able to identify and palpate the laryngeal prominence of the thyroid cartilage, the cricoid

cartilageand the first few tracheal rings (refer to your atlas for an image).

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Neck 2

Step 3

Carotid Triangle of the Neck


The carotid triangleis a subdivision of the infrahyoid region of the anterior triangle of the neck (refer to

your atlas for an image). Itis bounded by the:

superior belly of the omohyoid muscle (anteroinferior)

posterior belly of the digastric muscle (anterosuperior)anterior border of the sternocleidomastoid muscle (posterior)


of the neckCarotid triangle

The pulse of the common carotid arterycan be palpated in this region. The common carotid artery divides

into the internal and external carotid arteriesat the level of the superior border of the thyroid cartilage. Near

this bifurcation the carotid body a chemoreceptor that monitors O2 levels in the blood, lies wedged between

the internal and external carotid arteries, and the carotid sinus, a baroreceptor that responds to changes in

blood pressure, lies embedded in the muscular wall of the common/internal carotid artery. Reposition the

infrahyoid and SCM muscles and visualize the carotid triangle.

TIP:The external carotid artery gives many branches in the neck. The internal carotid artery

gives no branches in the neck.

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Deep to the SCM musclethe internal jugular vein, common carotid artery and vagus nerve lie within the

carotid sheath (refer to your atlas for an image). In an earlier step you severed the inferior attachment of SCM

and reflected the muscle far enough to see the omohyoid muscle. Now you need to fully reflect SCM, all the

way up to its attachment on the mastoid process. Pull SCM superiorly and use the small scissors to help clear

fascia from the deep surface of the muscle. Be careful not to damage the nerves of the punctum nervosa.

(Spinal) accessory nerve (CN XI)

On the deep surface of the SCM, about 5 cm inferior to the mastoid process, the accessory nerveenters the

muscle (refer to your atlas for an image). The nerve is very thick at this point. Find it and clean it as far

superiorly as you can. It enters the neck by passing through thejugular foramen on the base of the skull. (Find

this opening on a model skull.) Find the branch of CN XI that descends across the posterior triangle of the neck

to innervate trapezius. You should be able to tug on that branch and wiggle the main trunk of the nerve.

Ansa cervicalis

(CC - common cartoid artery; IJV - internal jugular

vein)

Hypoglossal nerve (CN XII)

The internal jugular vein(IJV) should be visible once you have reflected the SCM. It is the most superficial

structure in the carotid sheath. It lies lateral to the common carotid artery but because it is larger in diameter

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than the artery, the vein conceals the artery (from this view). Cut the connection between the IJV and the facial

veinso you have better access to the deep structures (refer to your atlas for an image). Gently explore the

fascia of the anterior carotid sheath surrounding the IJV and common carotid artery and locate the ansa

cervicalis.This is a plexus of motor nerves from the ventral rami of C1-C3. The ansa cervicalis innervates the

infrahyoid muscles (refer to your atlas for an image). Follow the ansa branches to the omohyoid and

sternothyroid muscles to verify the relationship between the ansa cervicalis and the infrahyoid muscles. Then

follow the nerves superiorly and note that some pass lateral to the IJV (sometimes between the IJV and

common carotid artery). These branches are from C2, 3 and are called the inferior root of the ansa cervicalis.The branch running parallel to the carotid artery comes from C1 and is called the superior root (refer to your

atlas for an image).

Follow the C1 superior rootsuperiorly, past the point where the common carotid artery branches into internal

and external carotid arteries. Soon you will see it connected to a thick nerve that loops down into the carotid

triangle and, at the angle of the mandible, turns medially and crosses the external carotid artery and some of its

branches. This thick loop of nerve is the hypoglossal nerve (CN XII). It exits the skull through the

hypoglossal foramen (canal)(find this on a model skull, refer to your atlas for an image) and enters the floor

of the mouth superior to the mylohyoid muscle (suprahyoid region). There it provides motor innervation to the

muscles of the tongue.

Just inferior to the hypoglossal nerve lies the greater horn of the hyoid bone. Palpate this important

landmark then follow the hypoglossal nerveantereomedially cleaning away fascia as you go. Trace a very

slender nerve that appears to be a brnch of hypoglossal. It innervates the thyrohyoid muscle. This nerve is a

branch of C1 not hypoglossal!!

TIP:The hyoid bone has no bony articulations. Therefore it is very mobile. Palpate your own

hyoid bone using your index finger and thumb and move it from side to side. To find the hyoid

bone on yourself or a colleague, first find the superior border of the thyroid cartilage using the

laryngeal prominence as a landmark. Rest your thumb and index finger on the superior border of the

thyroid cartilage lateral to the laryngeal prominence. Now swallow. At the end of the swallow your

thumb and finger should feel a space above the thyroid cartilage and, superior to that, you should

feel the greater horns of the hyoid bone. Move your thumb and finger to the greater horns and glide

the hyoid bone medial-laterally between your fingers. This can be a little uncomfortable so be gentle

if you are palpating someone else.

Just superior to the hypoglossal nerve lies the posterior belly of the digastric muscle, the third border of the

carotid triangle(refer to your atlas for an image). This muscle will become clearer after the dissection of the

suprahyoid muscles.

As you clear away the fascia in the carotid triangle the common carotid arteryand its branches will become

more visible. Clean and identify two branches of the external carotid, the superior thyroid arteryand lingual

artery (refer to your atlas for an image). The superior thyroid artery descends anterior to the common carotid

artery to supply the thyroid gland. The lingual artery ascends from its origin and follows the hypoglossal nerve

to the tongue.

Using a small scissors, push the IJV and common carotid artery apart and look for the vagus nerve. It lies

within the carotid sheathposterior to the IJV and carotid artery (refer to your atlas for an image). Clean the

full extent of the vagus inferiorly and verify its identity by finding vagus in the ipsilateral thorax and tugging

on it. The vagus in the neck should wiggle.

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Common carotid artery

Now clean vagus as far superiorly as you can and look for the superior laryngeal nerve, a branch of the vagus

that innervates parts of the larynx. The easiest way to find superior laryngeal nerve is to find its largest branch,

the internal laryngeal nerve, and follow it back to the superior laryngeal. The internal laryngeal nerve pierces

the thyrohyoid membranejust deep to the posterior border of the thyrohyoid muscle (refer to your atlas for animage). Push away the posterior border of the thyrohyoid muscle and feel the thyrohyoid membrane in the

space between the thyroid cartilage and the hyoid bone. Look for the internal laryngeal nerve piercing the

membrane about 1-1.5 cm lateral to midline. It is quite a large nerve and is accompanied into the larynx by the

small superior laryngeal arteryusually a branch of the superior thyroid artery (refer to your atlas for an

image). You will see these structures again during dissection of the larynx. The internal laryngeal nerve

provides sensory innervation to the larynx above the level of the vocal cords. Once you have found the internal

laryngeal nerve, follow it superiorly, gently pushing structures aside as you go, and find the superior laryngeal

and vagus nerves.

TIP:You may want to tilt the cadavers head back and turn it to one side in order to have better

access to the deep parts of the carotid triangle. You can do this by putting a low block under theshoulder of the cadaver on the side you want to work on. Then reposition the head.

The superior laryngealnerve typically arises from the vagus nerve superior to the origin of the facial artery

from the external carotid artery. It descends a short distance then divides into internal and external laryngeal

nerves at the point where it crosses the internal carotid artery. Follow the superior laryngeal nerve back down

the neck and look for its other branchthe very thinexternal laryngeal nerve.External laryngeal descends on

the external surface of the larynx to innervate the cricothyroid musclepostioned between the cricoid and

thyroid cartilages (refer to your atlas for an image). If you havent previously reflected the sternothyroid

muscle from its superior attachment, do so now and verify the path of the external laryngeal nerve to the

cricothyroid muscle. Preserve this relationship for study again during dissection of the larynx.

Now that you have cleaned and loosened the superior region of carotid triangle, re-examine the common

carotid artery.Just at its branch point identify a dilation - the carotid sinus (refer to your atlas for an image).

In this region the smooth muscle of the artery contains baroreceptorsthat transmit information about blood

pressure to the brain via CN IX, the glossopharyngeal nerve. (You can't see the baroreceptors. They are

embedded in the arterial wall.) Straddling the bifurcation of the common carotid artery into internal and

external carotid arteries is another special structure - the carotid body. This small dark brown mass is

connected to the arteries by many capillary-sized vessels from which it samples blood. It sends information

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about the chemistry of the bloodto the brain via CN IX. You will look for CN IX at a later time and from a

different vantage point. Then you can follow it back to the carotid structures.

Branches of the external carotid artery

Now look for several more branches of the external carotid artery (refer to your atlas for an image). Youhave already found the superior thyroid, internal laryngeal and lingual branches. Near the point where the

posterior belly of the digastric musclecrosses the external carotid artery look for the facial arterytraveling

medially and the occipital artery traveling posteriorly. The facial artery will dive under the submandibular

glandand loop back to cross the inferior border of the mandible (refer to your atlas for an image). It might be

easier to follow the facial artery from the mandible back to the carotid.Do not remove the submandibular

gland, just loosen it and push it aside to follow the artery.

The occipital arterygives a branch to the SCM then dives deep to the muscles attached to the mastoid process

before ascending on the base of the occipital bone. It is visible in the apex of the posterior triangle of the neck.

Look for the small ascending pharyngeal arteryjust superior to the bifurcation of the common carotid artery.

More superior branches of the external carotid will be dissected in a later step.

TIP:Expect to find variations in the branches of the external carotid artery and the tributaries

of the internal jugular vein!

Veins accompanying these arteries empty into the IJV. Identify the common facial, lingual and superior

thyroid veins,then carefully remove them from the dissection field.

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Neck 2

Step 4

Submandibular and Submental Triangles


The borders of the submandibular (digastric) triangleare:

Anterior: anterior belly of the digastric muscle

Posterior: posterior belly of the digastric muscle

Superior: inferior border of the mandible


of the neckSkull

In order to appreciate the structures that you will dissect in this step, begin by looking at the inferior and lateral

aspects of the temporal boneof the skull and the internal aspect of a mandible.Identify two projections

from the temporal bone - the large mastoid processlocated posterior and inferior to the external acoustic

meatus; and the styloid processa long narrow projection about 0.5 cm anterior and medial to the mastoid

process (refer to your atlas for an image). In many of the real skulls in your bone boxes the styloid process has

broken off. The plastic skulls in the lab are usually intact.

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Digastric and submandibular fossae Mylohyoid line and groove

On the internal aspect of the mandibleidentify three depressions and one raised element (refer to your atlas

for an image). The digastric fossa(e)lies on the internal surface of the anterior inferior region of the mandible

on each side of the midline mandibular symphysis. These fossae are the attachments sites for the anterior

belly of the left and right digastric muscles. The mylohyoid lineis a somewhat obliquely oriented ridgeabout 3 cm long located along the middle third of the body of the mandible (refer to your atlas for an image).

It is the attachment site for the mylohyoid muscle- a transversely oriented muscle with a midline raphe. The

mylohyoid muscle supports the floor of the mouth.

Inferior and parallel to the mylohyoid line is the submandibular fossa. This depression houses the

submandibular gland. The mylohyoid grooveis located on the internal surface of the angle of the mandible. It

descends for about 1.5 cm from the mandibular foramenand carries the nerves and vessels that supply the

mylohyoid muscle and the anterior belly of the digastric. The mandibular foramen and its contents will be

studied in a later lab.

Submandibular triangle Hypoglossal nerve (CN XII)

Now return to the cadaver and continue your dissection of the anterior triangle of the neck. Identify the borders

of the submandibular triangleand the submandibular glandthat lies within the triangle (refer to your atlas

for an image). Clean the anterior and posterior bellies of the digastric muscle.Deep to the anterior bellyof

the digastric, identify the mylohyoid muscledistinctive for its transversely oriented fibers.

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Identify the submandibular gland. It is larger than what you see on the surface. It wraps around the posterior

border of the mylohyoid muscle. Thus, its superficial portion lies inferior to the mylohyoid muscle while its

deep portion lies superior to the mylohyoid between the mylohyoid and hyoglossus muscles. Its duct passes

anteriorly and medially to open onto the floor of the mouth. The submandibular gland has relations to the facial

artery and vein as well as the lingual and hypoglossal nerves. Detailed dissection of the gland and duct will be

done with dissection of the oral cavity.

Loosen the submandibular glandfrom its surrounding fascia but do not remove it from its location.Separate the facial artery and veinfrom the submandibular gland. Note that branches of the facial artery

supply the gland. Review the origin of the facial artery from the external carotid artery.

Identify the intermediate tendonthat joins the anteriorand posterior bellies of the digastric muscle (refer to

your atlas for an image). It is anchored to the body and greater horn of the hyoid bonevia a fibrous sling of

pretracheal fascia. Examine the posterior belly of the digastric muscle near the intermediate tendon and note

that it is straddled by the stylohyoid muscle (refer to your atlas for an image).Carefully push the fibers of the

stylohyoid away from the digastric and follow it superiorly as far as you can. Stylohyoid originates from the

styloid processof the temporal bone. You can probably feel the tip of the styloid process if you slide your

finger superiorly along the muscle. Follow the posterior belly of the digastric to the mastoid process.

TIP:The anterior and posterior bellies of the digastric muscle have different embryological

origins. This explains the fact that they are innervated by different nerves! The mylohyoid

muscle and anterior belly of digastric receive a branch of CN V3 (nerve to mylohyoid), the

stylohyoid muscle and posterior belly of digastric are innervated by CN VII.

Locate the hypoglossal nerve (CN XII)in the carotid triangle and follow it into the submandibular triangle

(refer to your atlas for an image). Confirm that the nerve travels superior to the mylohyoid muscle.Its pathway

inside the oral cavity will be dissected later.

Pull the anterior belly of the digastricmedially and identify the nerve to the mylohyoid(branch of CN V3)

(refer to your atlas for an image). The nerve lies against the mylohyoid muscle which it innervates and sends a

branch anteriorly to innervate the anterior belly of the digastric muscle.

Submental triangle

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Identify thesubmental triangle (refer to your atlas for an image).Its borders and floor are the:

Anterior belly of the left and rightdigastric muscles(left and right lateral)

Body of the hyoid bone (base)

Two mylohyoid muscles(floor)

Find and clean all of the muscles that form the borders and floor of the submental triangle the anterior belly

of the right and left digastric muscles and the two mylohyoid muscles. Identify the raphe that joins the right andleft mylohyoid muscles.Look for the nerve to the mylohyoid muscle. It is a branch of CNV3.

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Neck 2

Step 5

Thyroid and Parathyroid Glands


Return to the midline of the neck and reexamine the thyroid gland. It lies inferior to the thyroid and cricoid

cartilages (refer to your atlas for an image). Its right and left lobes are united in the midline by an isthmus.

Note that the isthmus lies anterior to the 2nd to 4th tracheal rings. The isthmus may give rise to apyramidal

lobethat extends superiorly. Determine if this is the case in your cadaver. Approximately 50% of people have a

pyramidal lobe.

Thyroid gland

Identify the superior thyroid artery, a branch of the external carotid artery (refer to your atlas for an image).

To find the inferior thyroid artery, pull one lobe of the thyroid gland anteriorly away from the trachea. Don't

remove it, just pull it forward. The artery should be visible. Trace it to its origin from the thyrocervical trunk.

Some people (10%) have a thyroid ima artery. This unpaired artery usually arises from the brachiocephalic

trunk (refer to your atlas for an image).

Look for superior, middle and inferior thyroid veinsdraining the thyroid gland (refer to your atlas for an

image). These veins form a venous plexus over the anterior surface of the gland. The superior thyroid veins

parallel the superior thyroid arteries and drain into the internal jugular veins (IJV). The middle thyroid veins

parallel the inferior thyroid artery and also drain into the IJVs. The inferior thyroid veins drain the inferior

aspects of the gland into the brachiocephalic vein.

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Left recurrent laryngeal nerve relation to thyroid

glandThyroid gland reflected

Cut through the isthmusof the thyroid gland and reflect the right and left lobes laterally. You will find a

fascial bandthat connects the capsule of the gland to the 1st tracheal ring (refer to your atlas for an image).

Clean along the trachea on the left side of the body and find the recurrent laryngeal nerveascending toward

the larynx. Verify its identity by returning to the thorax and following the left recurrent around the aorta and

into the superior thoracic aperture.

On the right side, find the right recurrent laryngeal nerveby following the vagus nerve toward the superior

thoracic aperture. The right recurrent nerve recurs around the subclavian artery (refer to your atlas for animage). Clean the region until you can verify this pathway.

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Parathyroid glands (posterior view)

Reflect one of the thyroid lobes anteriorly and medially so you can inspect its posterior surface. Look for the

parathyroid glandswhich are small (approximately 0.5 cm in diameter) dark masses located between the

capsule and the sheath. They are often hard and very smooth. There are usually 2 parathyroid glands on each

side, but there may be 1 to 3 (refer to your atlas for an image).

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Neck 2

Step 6

Root of the Neck


The root of the neckis the junction between the thorax and the neck. It is sometimes called the

thoracocervical region. It contains the superior thoracic aperturethrough which all of the important

structures running between the thorax and the head pass. The boundaries of the root of the neck are:

Manubrium of sternum (anterior)

1stand their costal cartilages (lateral)

Body of T1 vertebra (posterior)

On the left side only, sever the internal jugular vein2 cm inferior to the bifurcation of the common carotid

artery and reflect it anteriorly. It is not usually necessary to cut the common carotid artery but check with yourlab instructor if you have any questions about your cadaver. DO NOT CUT THE VAGUS OR PHRENIC

NERVES!!Use a dissecting pin or needle probe to hold the IJV anteriorly so you can explore the root of the

neck.

Subclavian vein

Look for the thoracic ductthat arches over the left subclavian artery and terminates in the left venous angle

formed by the joining of the left subclavianand internal jugular veins (refer to your atlas).Return to the

thoracic cavity and find the thoracic duct there. Free it along its path toward the left venous angle until you can

tug on it in the thorax and see it wiggle in the root of the neck. Take great care in dissecting the thoracic ductbecause it is easily torn.

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Vagus and phrenic nerves

Identify and clean the distal cervical parts of the vagusand phrenic nerves.Note that the phrenic nerve is

intimately applied to the anterior surface of the anterior scalene muscle (refer to your atlas for an image). Whatis its relation to the prevertebral fascia? Follow both the phrenic and vagus nerves along their full paths through

the neck and into the thorax. Describe their relation to each other at three points: the level of C6, in the root of

the neck, and in the superior thorax.

Thyrocervical trunk

Note that the transverse cervicaland suprascapular arteriespass superficial to the phrenic nerve and anterior

scalene muscle (refer to your atlas for an image). Trace these arteries back to their origin from the

thyrocervical trunk(occasionally the subclavian artery). Identify the inferior thyroid arteryas it arises from

the thyrocervical trunk. Follow it as it passes posterior to the carotid sheath to supply the thyroid gland.

TIP:Expect to find variations in the branches of the thyrocervical trunk and subclavian artery!

Clean the subclavian arteryworking medially from the thyrocervical trunk. Find the vertebral artery, the

first and largest branch of the subclavian artery (refer to your atlas for an image). It ascends for a short distance

in a triangular space bounded by the anterior scalene and longus colli muscles before it dives deep to enter the

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transverse foramen of C6. It will pass through the transverse foramina of C1-C6 before it enters the skull

through the foramen magnum.

Vertebral and internal thoracic arteries, thyrocervical trunk

Find the internal thoracic arterywhere it arises from the subclavian artery opposite to the thyrocervical trunk(refer to your atlas for an image). The internal thoracic artery descends into the thorax adjacent to the sternum,

posterior to the first 6 costal cartilages and supplies the anterior thoracic wall.

Now follow the subclavian artery laterally. Where it passes between the anterior and middle scalene muscles it

gives rise to the costocervical trunkwhich divides into the superior intercostal and deep cervical arteries

(refer to your atlas for an image). They supply the first two intercostal spaces and the deep cervical muscles

respectively.

Finally, clean along the anterior surface of the cervical vertebrae parallel and medial to the vagus nerve.

Identify the cervical sympathetic trunk and ganglia(refer to your atlas for an image).

TIP:The vagus nerve and sympathetic trunk can sometimes look similar. Be sure that you

identify some distinguishing characteristics of each so you can easily tell them apart!

The middle cervical ganglionlies near the upper border of C6. It is not always very distinct but you may see

small nerves descending from it into the thorax. The inferior cervical ganglionlies at the level of C7-T1.

Sometimes it fuses with the T1 ganglion. Then it is called the stellate ganglion. The superior cervical ganglion

will be identified in subsequent dissections.

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Osteology

General Overview

Cranial Osteology Conference: Skull

Introduction

The following outline provides a guide to the important cranial structures that you need to know in order to

understand and appreciate the clinical anatomy of the head. It is best to become familiar with these structures

on the dry skullprior to beginning dissection of the soft tissue of the head. Refer to your text or atlas to

identify the structures listed below.

The structures that will be the focus of the Cranial Osteology Conference are listed in bold. They are organized

according to visible perspective of the skull (superior view etc.) Many structures can be seen from more than

one perspective. However, in the following list they are bolded only in their most visible perspective of the

skull. Soft tissue structures related to the bony structures are listed in italics. Realize that in most cases, the

appearance of each foramen in the dry skull is quite different from that in the cadaver (or living person!)

because many of the foramina are covered by dura or other soft tissue structures.

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Exterior of the Adult Skull

I. Superior View (Norma Verticalis) (Childs skull - refer to your atlas for an image).

Child's Skull (superior view)

Bones1.

frontal bone

parietal bones (paired)

occipital bonesutural bones (variable): wormian bones - most often found in lambdoid suture; a lar

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Head and Neck Dissector