60 



CO .MP AR ATI V K ANATOMY . 



arises first, and is distinguished from the other or post-oral arches 

 as the mandibular arch. The post-oral arches only, function as ^ill- 

 bearers in the- adult lisli : even the first of these, the hyoid, which 



j\r 



FIG. -i'3. DIAGRAM SHOWING TIIK UF.LATIONS OF THE KMI;KY<>MI- 



SKELETON. 



A", nasal capsule; A, eye; 0, auditory capsule ; Tr, trabeculie, which, from 



bent down anteriorly (t), a^ain extend forwards in a line with tin- vertebral 

 axis; M, Meckel's cartilage; Qx, quadrate; ///, hyoid nn-h : /'. /', branchial 

 arches, between which are seen the gill-clefts; S, spiracle; (.''. i.'o, basi-liy.'id 

 and basi-branchials. 



i.s supplied by the facial nerve, becomes modified from those 

 lying behind it: the latter, <>r branchial arches proper, an- 

 supplied by the glossopharyngeal and vagus. Nevertheless, 



I'TTTJTX 



| M;; . 47. SKMI-IU \<;I;AMMATIC Ficrr.r. HF AX ELASMOBRANCH SKULL, SHOWING 

 TIM. RELATIONS OJ nn: SKG.MF.NTAI. CKANIAL XKKVK.S. 



J\', nasal capsu^r : ./, eye ; O. nudifory capsule : Tr, tralirruli : Q and /''.'. 



ami palatopterygoid, whic-h an; bound to tlic trabecula by li.'.vun.'iit at i : i/. 

 Meckel's cartilage; t, i 1 , labial cartilages ; 27, hyomandibular ; f , hynid arch; 

 a to e, branchial arches, between \\hi.di tin- u'ill-r].-l'ts (/ to /") are seen : X, 

 spiracle : <', iinf.clM.nl : //', //", vertebra : /', tn.-cminal nerve, and 1, 2, 3, its 

 tlnvr main divisions : /.',-'. its palatine brancli ; /'//, facial DCTVe ; /,'/', its 

 palatine br.uieli ; IX, gloBBOphAryngeal ; A', va-us. 



everything goes to prove that formerly a time existed in \vliidi all 

 the visceral inches must have borne gills, and in the enil>i\..sof 

 Elasmobranclis they even still do so. 



Originally unsegmented in most cases, the individual arches 

 may become br< k-u up into ditfeivnt (as many as four) pieces, of 



