. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates. 292 COMPARATIVE ANATOMY se ass and these lie in planes roughly at right angles to one another. They are distinguished as the anterior vcrf/m/, the posterior vertical, and the horizontal (external) canal (Fig. 213). The first and last- named arise from the portion of the utriculus known as the recessus utriculi, and at its origin each has a vesicle-like swelling or ampulla, enclosing sensory cells. The posterior canal also arises with an ampulla from a prolongation of the utriculus. The other end of the horizontal canal op
. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates. 292 COMPARATIVE ANATOMY se ass and these lie in planes roughly at right angles to one another. They are distinguished as the anterior vcrf/m/, the posterior vertical, and the horizontal (external) canal (Fig. 213). The first and last- named arise from the portion of the utriculus known as the recessus utriculi, and at its origin each has a vesicle-like swelling or ampulla, enclosing sensory cells. The posterior canal also arises with an ampulla from a prolongation of the utriculus. The other end of the horizontal canal opens by a funnel-shaped enlargement into the utriculus, while that of the anterior and of the posterior canal unite to form a common tube, the so-called canal commis- sure (sinus superior), which also opens into the utriculus. Concretions composed mainly of carbonate of lime are present in the regions of the various nerve end-plates of the auditory organ in all Vertebrates. These otoliths, which arise in the epi- thelium lining the organ, and are then set free into its cavi- ties, present the greatest variety both in form and size. The largest and most massive ones are seen in Teleosts. They either consist of a single mass, otoliths are present regions of the laby- rinth. The sensory epithelium, to which the branches of the audi- tory nerve are distributed, is utriculo-saccular canal; de~, se, ductus Situated in the following parts of and saccus endolymphaticus, the the membranous labyrinth: (1) the former arising from the sacculus at three ampulla? of the canals, ill each of which the auditory cells are situated on a ridge (crista acustica) projecting into the lumen (Fig. 214); (2) the utriculus and the recessus utriculi; (3) the sacculus and lagena, or rudiment of the cochlea; (4) the rudimentary macula acustica neglccta, which in Fishes, Birds/ and Reptiles is situated on the floor of the utriculus close to the sacculo-utricular canal, in Amphibians on the inner side of the s
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