File:The American journal of anatomy (1901) (14803847273).jpg

Identifier: americanjournalo06wist (find matches)
Title: The American journal of anatomy
Year: 1901 (1900s)
Authors: Wistar Institute of Anatomy and Biology Association of American Anatomists
Subjects: Anatomy Anatomy
Publisher: Baltimore, MD : (s.n.)
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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the latter case it is a matter of simultaneousgrowth of all three structures. A resume of the development of the labyrinth is presented in the formof a diagram in the adjacent Fig. 4, which illustrates the successive stepsby which the simple ea-r vesicle enlarges and becomes differentiated intothe group of connected individual compartments which characterize theadult ear. The ear vesicle very early (6-7 mm. long, 3^ weeks) assumes the formof two communicating pouches, the vestibular pouch, with its endolym-phatic appendage, and the cochlear pouch. The first gives origin to thesemicircular canals, ampullae, utricle, and saccule. The semicircularcanals, in consequence of the approximation and absorption of the inter-vening wall of the vesicle, make their appearance between the fourth andfifth weeks, 9-14 mm. (only one is shown in the diagrams). Thatportion of the vestibular pouch that is not involved in the formation ofthe canals and their ampullae may be called atrium, to indicate that
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« ^ ay <V <i^ a n^tw w d O rH O 154 Development of Ear and VII-VIII Cranial Nerves it forms at this time a common meeting place into which open the differentcompartments, including the endolymphatic appendage. At six weeks,20 mm., the atrinm becomes separated into an upper and lower divisionby an ingrowth of its wall, thus forming the utricle and saccule. Thispartition continues inward in such a way as to split the orifice of theductus endolymphaticus, the divided ends of which form the ductusutriculo-sacculus. The cochlear pouch opens directly into the atrium,and as the development proceeds it can be seen that it is into that partof the atrium which is destined to form the saccule. At the fifth week,14 mm., a beginning constriction appears between the cochlea and thesaccular region. This constriction corresponds to the ductus reuniensand gradually narrows down until in the adult in many cases the com-munication between cochlea and saccule is obliterated. It is very ap-parent t

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