86 



COMPARATIVE ANATOMY 



supported by various skeletal elements, amongst which may 

 be mentioned a ring-like cartilage (an.c) around the margin 

 of the dome-shaped oral funnel, between the dorsal side of 

 which and the brain-case are a couple of large overlapping carti- 

 lages (a.d.c, p.d.c} : the tongue is supported by a long, lingual 

 cartilage (Ig.c), and besides the other elements shown in Fig. 64, 

 cartilages are present in the velum at the base of the oral funnel. 

 On the mucous membrane covering the annular and lingual 

 cartilages inside the oral funnel are a number of horny teeth. 

 The fibro -cartilaginous olfactory sac is unpaired, and opens on the 

 dorsal surface of the head by a single nostril. The visceral 

 skeleton also shows many exceptional peculiarities : it consists of 

 a series of unsegmented rods produced into short processes and 



Nv.S 



ex.b. 



brr 1 



fiy.cn. 



c&.br 



FIG. 05. SKULL OF DOGFISH (Scyllium canicula). (From T. J. Parker's 

 Biology, after W. K. Parker. ) 



aud.cp, auditory capsule; br.a, 1 5 branchial arches ; br.r, br.r', branchial rays 

 arising from the hyoid and branchial arches; Cr, cranium; ex.br, extra- 

 branchial cartilages ; hy.cn, ventral part of hyoid arch ; hy.m, hyoman- 

 dibular ; ll>, labial cartilage; ff/.fy', ligaments supporting the jaws from 

 the cranium ; Lj, MeckePs cartilage; Nv. 2, optic foramen ; Nv. 5, foramen 

 for trigeminal and facial nerves; olf.cp, olfactory capsule; or, orbit; r, 

 rostral cartilage ; up.j, palatoquadrate. (The spiracular cartilage is not 

 indicated.) 



connected with one another by longitudinal bars, the whole forming 

 a delicate cartilaginous basket-work : the last bar is connected 

 with a cartilage in the walls of the pericardium. This basket- 

 work has a very superficial position. 



In Myxine the branchial skeleton is rudimentary, and amongst 

 other peculiarities, the long nasal passage is surrounded by 

 cartilaginous rings and communicates with the pharynx by a 

 naso-palatine duct. 



No fossil Cyclostomes are known, but Palceospondylus gunni 



