A manual of otology for students and practitioners . FENESTRA OVALISLOSED BY STAPES Fig. 3.—Vertical section of the external auditory meatus and tympanum. (Gerrish.) EXTERNAL EAR 21 posteriorly (Figs. 2 and 3). The osseous canal is formedprincipally by the outgrowth of the tympanic ring. Atbirth this ring forms an incomplete circle (Fig. 4). Thepart between the ends of the ring is called the segmentof Rivinus, and is filled in by the squamous portion ofthe temporal bone. In the development of the bone thisgrows pari passu with the outgrowth from the tympanicring and completes the canal above.
A manual of otology for students and practitioners . FENESTRA OVALISLOSED BY STAPES Fig. 3.—Vertical section of the external auditory meatus and tympanum. (Gerrish.) EXTERNAL EAR 21 posteriorly (Figs. 2 and 3). The osseous canal is formedprincipally by the outgrowth of the tympanic ring. Atbirth this ring forms an incomplete circle (Fig. 4). Thepart between the ends of the ring is called the segmentof Rivinus, and is filled in by the squamous portion ofthe temporal bone. In the development of the bone thisgrows pari passu with the outgrowth from the tympanicring and completes the canal above. This takes place 1 forsquamousporfion,includingzygoma :Sd month. 1 for ti/mpanicplate. 6 for petrous and mastoid portions. 2 for styloid process. Fig. 4.—Tympanic ring. (Gray.). in extra-uterine life. At birth there is no osseous canal,the tympanic ring, and therefore the drum membraneattached to it, lie practically on the surface. The inclina-tion of the drum head is as great or slightly greater thanin adult life, its external surface being directed downward,forward, and outward. The membranous canal is attacheddirectly to the tympanic ring and its direction is upwardand outward, the auricle being placed higher on thesquama than in the adult. 22 ANATOMY AND PHYSIOLOGY OF THE EAR The nerve supply of the external auditory canal isderived from the auriculotemporal, the auricularis mag-nus, and the pneumogastric through its auricular branch(Arnolds nerve). It is claimed that the facial suppliessensory and trophic filaments to the external auditorycanal and auriqle. This claim is based largely uponpathological investigations which are discussed underHerpes Zoster Oticus. Tympanic Membrane.—The tympanic membrane formsthe fundus of the external canal and part of
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