Paper - Some features of the auditory apparatus of a 16 mm human embryo
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Jenkins GJ. Some features of the auditory apparatus of a 16 mm human embryo, as shown in a reconstruction model. (1910) Proc R Soc Med. 3 :34-5. PMID: 19974624
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Some Features of the Auditory Apparatus of a 16 mm Human Embryo (by the Wax-plate method of Born)
By G. J. Jenkins, F.R.C.S.
The embryonic tubercles of the pinna have fused, but are still indicated. The external auditory meatus is expanded internally. In the model the plug of epithelial cells has been removed to show the form of the meatus.
The labyrinth: The vestibule is compressed laterally and is somewhat quadrilateral in form. The semicircular canals are in an advanced stage of development compared with the cochlea, which is represented by a simple tube turning on itself at its tip. The cochlear element of the labyrinth lies close to the roof of the pharynx, considerably internal to the oriﬁce of the primitive Eustachian tube, and comparatively close to the sagittal plane. The ductus endolymphaticus is large and long.
The region of the middle-ear tract : The Eustachian tube, tympanic cavity, and antrum are represented by the ﬁrst pharyngeal pouch in its more or less primitive condition. Superiorly, the pouch is forming an acute ﬁssure, and at its outer extremity is turning upwards to invade the mesoblast between the labyrinth and the external auditory meatus. Incus, malleus, and Meckel’s cartilage are represented as one continuous mass. Microscopically Meckel’s bar is cartilaginous in the lower part, but malleus and incus are still in the mesoblastic state and diﬂerentiated only by concentration of cells. The process from the bar in backward direction is the great process of the malleus. The incus has a thin process backwards and inwards, to fuse with the mesoblastic anlage of the stapes. The articulations have not yet been diﬁerentiated. The hyoid bar—in a prechondral stage—is seen passing upwards on the inner side of the facial nerve. The upper extremity of the hyoid bar bifurcates, the anterior portion being directly continuous with the stapes. The facial nerve lies in the fork so formed. There is a large vein lying to the outer side of the horizontal portion of the seventh cranial nerve, to the inner side of the malleus and incus, and below the external semicircular canal. It is connected posteriorly with the internal jugular vein, and anteriorly with a venous plexus internal to the Grasserian Otological ganglion. There is another large sinus channel, in the position somewhat of the petro-squamosal sinus, lying above the semicircular canals.
Mr. Jenkins also showed sections (10 μ) of a chip removed at a complete post-aural operation from the mastoid below and to the outside of the antrum, showing columnar cells of the lining membrane of the cells of the suture between the squamo-zygomatic and petro-mastoid elements of the mastoid process. He also showed specimens of sections (l0 u.) of thenormal adult mastoid, in which pavement epithelium lined the air-cells.
Mr. SCOTT said he had the privilege of being acquainted with Mr. Jenkins’s splendid work, which represented a move in the right direction; and he hoped that ultimately they would be able to reproduce specimens of pathological conditions by the same process.
Mr. JENKINS, in reply, said the magniﬁcation in this case was 50 diameters. The ossicles at that stage were simply concentrated mesoblast. The stapes was ring—like, the incus was particularly small, and the malleus large. The model was of a period before the synovial cavities in the body appeared. There was a large vein passing across the surface of the labyrinth in the position of the middle-ear tract, and he had not found such recorded in any book on embryology. Probably the anterior part of that vein persisted through life, but it was seen comparatively late in foetal life.
Cite this page: Hill, M.A. (2020, July 10) Embryology Paper - Some features of the auditory apparatus of a 16 mm human embryo. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_Some_features_of_the_auditory_apparatus_of_a_16_mm_human_embryo
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