An introduction to the study of the comparative anatomy of animals . ger space, the posteriorchamber of the eye, filled with a gelatinoid material, thevitreous humour. The sclerotic is lined by a black pig-mented layer called the choroid, which is continued in frontinto the iris. Inside of this, lining the chamber of the eye, is adelicate transparent membrane, the retina, on which theramifications of the optic nerve are spread. It is the sensitive Digitized by Microsoft® 7° COMPARATIVE ANATOMY portion of the eye, and the cornea, iris, lens, etc., are structuresadapted to focus the hght upon it
An introduction to the study of the comparative anatomy of animals . ger space, the posteriorchamber of the eye, filled with a gelatinoid material, thevitreous humour. The sclerotic is lined by a black pig-mented layer called the choroid, which is continued in frontinto the iris. Inside of this, lining the chamber of the eye, is adelicate transparent membrane, the retina, on which theramifications of the optic nerve are spread. It is the sensitive Digitized by Microsoft® 7° COMPARATIVE ANATOMY portion of the eye, and the cornea, iris, lens, etc., are structuresadapted to focus the hght upon it. The frogs ear is embedded in the periotic capsule, which, aswe have seen, is largely cartilaginous, with an anterior ossifica-tion, the pro-otic. The essential organs of hearing are deeplyembedded in the cartilage, and only communicate with thesurface by an accessory apparatus consisting of the tympaniccavity, the eustachian tube, and columella. The tympanic cavity, bounded externally by the tympanicmembrane, is seen, after removal of the latter, as a shallow,. Fig. right membranous labyrinth of the frogs earseen from the inner side. U, utriculus, from whichspring ace, the anterior semicircular canal withits ampulla aa ; pec, the posterior circular canalwith Its ampulla a7np; , the externalhorizontal semicircular canal, with its ampullaavtp, represented as showing through the trans-parent walls of the utriculus ; ^, the sacculus; de,the ductus endolymphaticus ; lag, lagena ; pbc,pars basilaris cochleEe. (Adapted from Retzius.) funnel-shaped cavity, lined by a pigmented mucous membrane,and communicating by the wide, short passage of the eusta-chian tube with the pharynx. The inner and deeper partof the cavity presents a small aperture leading into the innerear. This aperture, called the fenestra ovalis, is blockedby the enlarged cartilaginous end of a partly bony, partlycartilaginous rod, the columella auris, which traverses thetympanic cavity and is fixed by it
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