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 



ex.b. 



fiy.cn, 



F IG . 65. 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; Ib, labial cartilage; fyr.ty', ligaments supporting the jaws from 

 the cranium ; l.j, Meckel's cartilage ; Nv. 2, optic foramen ; Ni\ 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 



