The Skull II

Head & Neck – Lecture 2األعسم. جليل حيدر د

The Cranial Cavity

• VaultSutures:(Coronal, Sagittal & Lambdoid)-Impressions:arachnoid granulations, middle

meningeal aa., and superior sagittal sinus.

The Cranial Cavity• The Base of skull1- Anterior Cranial fossa2- Middle Cranial fossa3- Posterior Cranial fossa

We should know for each fossa:• Formed by? bones• Boundaries? walls• Contents?• Main Features? foramina

Anterior Cranial Fossa

• Formed by: orbital plates of the frontal bone, cribriform plate of the ethmoid, lesser wing of sphenoid & anterior part of body of sphenoid.

• Boundaries: inner surface of the frontal bone, lesser wings of the sphenoid on the sides and groove for the optic chiasma.

• Contains: the frontal lobes of the brain• Main features:• Foramen cecum (emissary vein)• Crista Galli (attachment of the falx cerebri)• Cribriform plate (olfactory bulbs and the olfactory nerves)• Anterior clinoid processes (attachment of tentorium cerebelli)

Middle Cranial Fossa

• Formed by: median part- body of sphenoid bone Lateral concavities - greater wing of sphenoid, squamous and

petrous parts of temporal bone.• Boundaries: Ant. lesser wing of sphenoid

Post. upper border of petrous part of temporal boneLat. greater wing of sphenoid, parietal bone and squamous

part of temporal bone.• Contains: the temporal lobes of the brain.

Middle Cranial Fossa

• Features: (7 foramina, median part, petrous part of temporal bone)1- Optic Canal: (ophthalmic a. & optic nerve) ―→ to the orbit.2- Superior orbital fissure: (superior ophthalmic vein, lacrimal, frontal, nasocilliary,

Abducent, Oclomotor & Trochlear nerves) ―→ to the orbital cavity.3- Foramen rotundum: (maxillary branch of Trigeminal (V) nerve) ―→ to the pterygo-

palatine fossa.4- Foramen ovale: (mandibular branch (sensory & motor) of trigeminal (V) nerve & the

lesser petrosal nerve) ―→ to the infratemporal fossa.

Middle Cranial Fossa

• Features: (7 foramina, median part, petrous part of temporal bone)5- Foramen spinosum: (middle meningeal artery) 6- Foramen lacerum:• Upper opening (Open - Internal Carotid Artery)• Lower opening (Closed – cartilage & fibrous tissue)7- Carotid Canal: (Internal Carotid Artery).

Middle Cranial Fossa

• Features: (7 foramina, median part, petrous part of temporal bone)The petrous part of temporal bone:• Medial groove for greater petrosal nerves • Lateral groove for Lesser petrosal nerve • Arcuate eminence: (semicircular canal in inner ear)• Tegmen tympani: (roof mastoid antrum, tympanic cavity and auditory tube)

Middle Cranial Fossa

• Features: (7 foramina, median part, petrous part of temporal bone)The Median part of Middle Cranial Fossa: (body of the sphenoid)• Sulcus Chiasmatis: a groove for optic chiasma.• Tuberculum sellae: (with middle clinoid processes)• Sella Turcica (Turkish saddle): a depression for the pituitary gland.• Dorsum Sellae: (with posterior clinoid process)

Posterior Cranial Fossa

• Formed by: Occipital bone, Mastoid part & post. half of petrous temporal bone.• Boundaries: superior border of petrous part of temporal bone & internal surface

of occipital bone.• Contains: cerebellum, midbrain, pons and medulla oblongata.• Main features: (Roof, 4 Foramina, 4 sinus grooves)• Roof: by a fold of dura called tentorium cerebelli that is attached to the upper

border to the petrous part of temporal bone.

Posterior Cranial Fossa

• Foramina: 1- Foramen Magnum: (Medulla Oblongata, Vertebral arteries and ascending roots

of accessary cranial nerve).2- Hypoglossal canal: (Hypoglossal nerve)3- Jugular foramen: (Inferior petrosal sinus, cranial nerves 9, 10 & 11 and sigmoid

sinus).4- Internal acoustic canal : (Vestibulo-cochlear nerve & Facial nerve)

Posterior Cranial Fossa

• Sinus grooves: these are deep impressions for the venous sinuses which are:1- Superior Petrosal sinus on upper border of petrous part of temporal bone.2- Inferior Petrosal sinus on lower border of petrous part of temporal bone.3- Sigmoid sinus which is S shaped on mastoid and petrous parts of temporal

bone.4- Transverse sinus on each side of internal occipital protuberance.

Bones of the Neck

1- Cervical Vertebrae (Spines)

2- Hyoid bone:

Cervical Spines

• They are 7 cervical vertebrae • Unique transverse foramen in the

transverse processes (vertebral vein and vertebral artery)

• There are: 3 Atypical (C1,C2 & C7)4 typical (C3-C6)All have transverse processes

Typical Cervical Spine

Features:1- The vertebral body is small and longer from side to side than anteroposteriorly; the superior surface is concave, and the inferior surface is convex.2- The vertebral foramen is triangular.3- The superior facets of the articular processes are directed superoposteriorly, and the inferior facets are directed inferoposteriorly.4- The spinous processes are short and bifid.5- The transverse process has anterior and posterior tubercles and in between a groove for spinal nerve.

Atypical Cervical Spine – C1

C1 vertebra (Atlas): • Ring-like shape• Encloses the odontoid process of C2 & Spinal cord with meninges• No Spinous process No Body• Has two lateral masses connected by anterior and posterior arches. • It has concave superior articular facets (Kidney shaped) to receive

the occipital condyles.

Atypical Cervical Spine – C2

C2 vertebra (Axis): • The strongest cervical vertebra. • Has two large, flat surfaces, the superior articular facets• Has tooth-like dens (odontoid process).• Both dens and the spinal cord are encircled by the atlas. The dens lies anterior to

the spinal cord and separated by the transverse ligament of the atlas. • It has a large bifid spinous process that can be felt deep in the nuchal groove .

Atypical Cervical Spine – C7

C7 vertebra: – It has long spinous process, which is not bifid. – Its transverse processes are large and directed downward which allow

differentiation from T1 Spine that has upward directed transverse process.

Hyoid Bone• It is a U-shaped bone that lies in the anterior

part of the neck (@ level of the C3)• It is suspended by muscles that connect it to:

• Mandible by mylohyoid, genohyoid &digastric muscles

• Styloid processes by stylohyoid muscle and ligament

• Thyroid cartilage by thyrohyoid muscle • Manubrium by sternohyoid muscle• Scapulae by omohyoid muscle

• The hyoid does not articulate with any other bone.

• The hyoid consists of a body, greater and lesser horns.

• Functionally, the hyoid serves as an attachment for anterior neck muscles and a prop to keep the airway open.

Good Luck