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 sacculus, and in Mammals undergoes a gradual 

 reduction and may even become obliterated. 1 The several portions 



1 In addition to these, there is a transitory Manila tlm-hi* rtuni< ////'.< situated 

 in the region of the sacculo-cochlear duct. 



RINTH OF A VERTEBRATE. 

 from the outer side. 



As seen 



ass, apex of the sinus utriculi superior; 

 ce, cp, anterior, external, and 



ca, 



posterior semicircular canals ;; aa, ae, 

 op, the corresponding ampullae : CMS. 



t ; I, recessus sacculi (lagena) ; rec, 



rtJCCSSUS 11 1 1*1 CIlll ', 6'j SUC/CUlllS ^?2 



sinus utriculi posterior ; ss, sinus 

 utriculi superior ; u, utriculus. 



