Text-book of the embryology of man and mammals / by Oscar Hertwig ; translated from the third German edition by Edward L. Mark.

Date:
1892
Catalogue details

Licence: Public Domain Mark

Credit: Text-book of the embryology of man and mammals / by Oscar Hertwig ; translated from the third German edition by Edward L. Mark. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    and are stretched out smoothly between the free margin of the lamina spiralis and the inner wall of the cartilaginous capsule. In this process the tympanic wall {C) comes to lie in the same plane as the lamina spii-alis, the vestibular wall (Iv) forms with the tympanic an acute angle, and the third wall {x) is everywhere in close contact with the perichondrium of the cartilaginous capsule. The epithelial lining of the membranous ductus cochlearis assumes very different conditions in the three corresponding regions of its wall. Whereas the epithelial cells of the vestibular and the outer walls become in part cubical, in part quite flat, those of the tympanic wall become elongated, and are in connection with the terminal fila- ments of the cochlear nerve ; they produce the complicated organ of CoRTi (C), which, like the auditory ridges and auditory patches of the ampullfe, the sacculus an^ utriculus, contains the terminal ends of the auditory nerve. The construction of the intricate cochlea approaches completion with the beginning of the process of ossification. The latter is accom- plished by two methods. First, the cartilaginous capsule ossifies in the endochondral manner, as does the whole cartilaginous os petrosum, of which it constitutes a small part. The osseous tissue thus formed is for a long time spongy and provided with large medullary spaces. Secondly, the previously mentioned fibrous connective-tissue layers— the partitions between the cochlear canals, the connective-tissue axis or the modiolus and the lamina spiralis—undergo direct ossifi- cation. At the same time compact bone-lamellje are laid down from within on the spongy bone-tissue formed from the cartilaginous capsule; these lamellae are formed, as Boettcher has shown, by the original perichondrium, which becomes the periosteum. Consequently the bony cochlear capsule, since it is produced by periosteal secretion, may be easily detached from the loose osseous tissue of endochondral origin during early post-natal years. (c) Develojjment of the Accessory Aj^paratics of the Organ of Rearing. {Middle and External Ear.) With the membranous and bony labyrinth, which are together called the inner ear, there is associated a subsidiary apparatus, in the same way that the eye-muscles, the lids, and the lachrymal ghmds and ducts are added to the eyeball. It is made up of structures which are wanting in the lower Vertebrates (Fishes), but, beginning to be developed in the Amphibia, become more and more complete in