196 



( 'COMPARATIVE ANATOMY. 



get a membranous and a bony labyrinth, and between them 

 a cavity (cavum perilymphaticum) tilled with a lymph-like fluid 

 (peri lymph). The cavity within the membranous labyrinth, 

 which 'also contains a tin id (endolymph), is spoken of as the 

 cavum endolymphaticum. 



With the exception of the Cyclostomi, three semicircular canals 

 are always present, and these lie in planes at right angles to one 

 another. They are distinguished as the anterior vertical, the 

 posterior vertical, and the horizontal (external) canals. 

 The first and lust-named (Fig. 161, &., II. B) arise from the 

 portion of the utriculus known as recessus utriculi (lic.ut.'), and 

 earh has a vesicle-like swelling or ampulla (8. A., If. A.} at its 



*e 



s.n. 



F.B. 



--F.A. 



FIG. 161. SEMIDIAGRAMMATIC FIGURE OF THE AUDITORY ORGAN OF A 

 TELEU.STEAN. (Modified from a figure of that of Murccna anyuilla by Hasse.) 



UL, utriculus ; Re.ut., recessus utriculi ; V.E., connecting-tube of the posterior ampulla. 

 (l'\A.)\ **, wide connecting-duct between the pars superior and pars inferior ; 

 S', sacculus ; O, cochlea; S.., F.B,, H.B., anterior and posterior vertical, and 

 horizontal canals; Co., canal commissure, with its apex ; S.A., H.A., F.A., 

 ampulla 1 , of the anterior, horizontal, and posterior canals ; D.f, ductus endo- 

 lymphati.-us. which arises from the point where the two tubes of the pars 

 superior of the labyrinth ai;d the opening of the horizontal canal ( x ) join one 

 another. 



origin. 



The posterior canal (F.B^) also arises with an ampulla 

 (F.A.} from a prolongation of the utriculus, described in Fig. 101 

 as the " connecting-tube " ( VM.'). 



The other end of the horizontal canal opens by a funnel-shaped 

 enlargement (Fig. 161, x) into the utriculus, while those of the 

 posterior and anterior canals fuse 

 tube, the so-called canal commissure 

 whii'-h also opens into the utriculus. 



The distribution of the branches of the auditory nerve and the 

 position of the sensory epithelium in the following parts of 



together to form a common 

 (sinus superior) (Co.~), 



the membianous labyrinth must now be considered: 1 (1) the 



1 Concretions composed mainly t>f earhnnate of lime are present in the regions 

 of the various nerve nid-plates uf the auditory oi<_an in all Vertebrates, as well as 

 in many Invertebrates. Tin sr "otoliths" presi-nt the greatest variety both in 



