72 



COMPARATIVE MORPHOLOGY OF VERTEBRATES 



the hyomandibular cartilage (fig. 6g, hnt), and a ventral portion, the 

 hyoid proper, which may subdivide into several parts (infra). In the 

 lower elasmobranchs the hyomandibular and the rest of the hyoid 

 arch are closely connected, but in the higher fishes the hyomandibular 

 becomes more separated from the ventral portion and tends to inter- 

 vene between the manidbular arch and the cranium, becoming a 

 suspensor of the jaws (figs. 71). Still higher it loses its suspensorial 

 functions, becomes greatly reduced, and apparently is subsidiary 

 to the sense of hearing (see auditory ossicles), or it may be lost, the 

 question not being decided. The hyoid proper becomes more or 



Fig. 72. — Branchial arches of (A) Heptanchus; (B), Chlamydoselache; and (C) 

 Cestracion; A and C after Gegenbaur, B after Garman. c, ceratobranchial; e, epibran- 

 chial; h, hyoid; hb, hyobranchial; he, hyoid copula; cbr, cardiobranchial (posterior 

 copula); p, pharyngobranchial; 1-7, branchial arches; m, Meckel's cartilage. 



less intimately connected with the arches behind and also is largely 

 concerned in affording a support for the tongue. 



The branchial arches are all similar to each other in the lower 

 vertebrates, but with the loss of branchial respiration in the higher 

 groups, they tend to become reduced, the reduction beginning behind. 

 Some may entirely disappear, others give rise to the laryngeal carti- 

 lages (see respiration) and the first may fuse with the hyoid. The 

 first arch is in the region of the ninth nerve; the others in that supplied 

 by the tenth. 



The elements of the branchial arches have the names (fig. 72), beginning 

 above, pharyngobranchial, epibranchial, ceratobranchial and hjrpobranchial, 

 the copulae (p. 69) usually being called the basibranchials. The elenjents of 



