Rom J Leg Med [2] 129 – 132 [2010] DOI: 10.4323/rjlm.2010.129 © 2010 Romanian Society of Legal Medicine

________________________ *) Corresponding author; Associate Professor, MD, PhD, Chair of Anatomy, University of Medicine and Pharmacy “Carol Davila”, Bd Eroilor Sanitari No 8, Bucharest, E-mail: popescu3dan@yahoo.com

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Ontogenetic landmarks of the organ of hearing in fetal age determination George Lupu, Daniel Popescu*, Victor Panus, Gabriela Popescu ____________________________________________________________________________

Abstract: Follwing the law of “Fundamental Biogenetics” or “The Revision Theory” according to “Ontogeny repeats philogeny” or “Ontogeny does not reproduce the ancestors but reminds their existence” we found that the appearance of the organ of hearing and conected to that the appearance of petrous part of the temporal bone follows the stages in philogenetic order. This organ reaches maximal developement in mammals, on which it is formed from three segments: internal, middle and external ear. The internal ear is ubiquitous in vertebrates, and on philogenetic scale it changes only its complexity. Middle ear appears starting with batrachians; to these, reptiles and birds, the tympanic membrane is linked to the fenestra vestibuli by one ossicle, the columela; and in mammals it is linked through a chain of ossicles formed by the hammer, the anvil and the stirrup. External ear appears in mammals, the tympanic membrain clogs slowly in a duct, the external auditory meatus.

Key words: fetal skull, temporal bone, periotic capsule, fetal age estimation

kull development in mammals runs three stages: the membranous, the cartilaginous and the osseous primary skull [1]. The membranous skull enhances from axial cephalic

mesenchymal, which throughout the weeks V and VI escorts up the notocordal process, sending links around the encephalon and through the cavities of the nose and the branchial arches.

From week VII starts the cartilaginous skull, but only to the base of the skull. In this phase the cartilaginous skull is formed by a posterior part (cordal or paleocranium) and an anterior part (precordal or neocranium).

Paleocranium is formed by a posterior part, segmented (paracordal cartilages) and an anterior part, not segmented; this last one appears from the mezenchim surrounding the otic plate (otic vesicle or otocist), respective the periotic capsule. Through condrification of the periotic capsule will be forming the petrous part of the temporal bone and its mastoid process [2].

The tympanic part of the temporal bone, the styloid process with the ossicles chain from the middle ear, respective the hummer, the anvil and the stirrup are also forming through the cartilaginous ossification from axial cephalic mesenchyma migrated in branchial arches, more exactly tympanic part, the hummer and the anvil from first branchial arch; the styloid process and the stirrup from the second branchial arch.

The squamous part of the temporal bone is forming through membrane ossification, a characteristic of the skull cap [3], [4].

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Material and method For this study 6 fetus, with

ages between 3 and 8 months, respectively 14, 17, 20, 24, 28 and 34 weeks, have been selected. Through specific techniques the soft parts of the cephalic extremity have been removed, and the skulls were kept for the study. These were analyzed and photographed in different angles with a high resolution camera, focused on the temporal bone.

Results, discussion Analyzing the digital

images of the temporal bone of fetus skulls we notice that:

- the boundaries between the component parts of temporal bone are visible in early fetal stage and at the end of it; also is seen a major change of both internal and external configuration of the temporal bone in this stage and important differences between fetal and adult skull.

- at the end of fetal stage the aspect of the skull is not in final configuration and not all the parts of temporal bone are completely configured; so, we observed the absence of mastoid process and styloid process at 34 weeks skull and consequently in new-born skull.

- we see the presence of ossicle chain in middle ear starting with fourth intrauterine month (17 and 20 weeks); keeping in mind that all those parts of the temporal bone are forming by chondral ossification [5], we can draw the conclusion that in new born, mastoid process and styloid process are cartilaginous (partially lost in macerating) and they ossify after birth, until they reach the age of two.

- at a 14 weeks skull, the internal ear is formed, the middle ear is just starting to appear without the ossicle chain. In the

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same time the tympanic ring, future to be tympanic part of the temporal bone is found in a lower position, almost horizontal and it is small. (Figure 1)

- at 17, 20 and 24 weeks skulls the middle ear is defined with walls, including tympanic membrane and three ossicles; the tympanic ring achieves an oblique sagital position tendentiously lateral. (Figure 2, 3, and 4)

- at 28 and 34 weeks skulls external auditory meatus is visible. In it dives the tympanic membrane and by its transparency it is seen the ossicles chain; the tympanic ring is lateral, bigger, longer and in a anteroinferior position to external auditory meatus. (Figure 5 and 6)

Conclusions 1) all three segments

of the organ of hearing are formed following the phylogenetic order, first internal ear, then the middle one and finally the external ear; the cartilaginous ossification around otic vesicle forms first a bony labyrinth and then partial tympanic cavity (at 14 weeks skull); final form of tympanic cavity walls (at 17 and 20 weeks skulls); external auditory meatus is the last element (at skulls after 24 week)

2) the three ossicles in middle ear are ossify and visible after the fourth month; in order to appear and ossify is medial to lateral, first outlined and ossified is the

Fig. 3 24 weeks fetal skull (lower surface of base of skull)

Fig. 3 28 weeks fetal skull (lower surface of base of skull)

Fig. 3 34 weeks fetal skull (lower surface of base of skull)

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stirrup (from second branchial arch), at 14 weeks skull, then the anvil and the hammer, both from first branchial arch. The handle of the hammer is the last to ossify, (after week 24) and to attach to the umbo of tympanic membrane.

3) the tympanic part of the temporal bone, outlined in a bony ring at 14 weeks skull, change its position, shape and dimension to final aspect, which is lateral, sagital; it participates in both external auditory meatus and mandibular fossa, and temporomandibular joint.

4) at the end of fetal stage, the aspect of the temporal bone is not final, and spaces are visible between component parts

5) the mastoid process and the styloid process are not configured in the nine month old skull; they ossify after birth, under the force of craniomotor muscles.

References 1. Andronescu A. Anatomia desvoltării omului. Embriologie medicală. Editura medicală, Bucureşti, 1987; 187-191 2. Sadler T. W. Langman’s medical embrilogy. Sixth edition. Williams&Wilkins. Baltimore, Maryland, 1990; 140-145 3. Cochard Larry R. Netter’s Atlas of human embryology. First edition. MediMedia, Inc. 2002; 192-194 4. Moore Keith L. The developing human. Clinically oriented embryology. Second edition. W.B. Saunders company.

Philadelfhia. 1977; 307-309 5. Dornescu G.T., Necrasov O. C. Anatomia comparată a vertebratelor. Vol l. Editura Didactică şi Pedagogică, Bucureşti,

1968.