6 4 



COMPARATIVE MORPHOLOGY OF VERTEBRATES. 



becomes greatly reduced, and apparently is subsidiary to the sense of 

 hearing (see auditory ossicles), or it may be lost, the matter not 

 being decided. The hyoid proper becomes more or less intimately con- 

 nected with the arches behind and 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 



FIG. 63. Ventral view of cranium and visceral arches of skate (Raia) after Gegenbaur. 

 cp, copula; h, hyoid; hnt, hyomandibular; la, upper labials; mk, Meckelian cartilage; 

 nc, nasal capsule; pg, pterygoquadrate; r, rostrum. 



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

 Some may entirely disappear, others give rise to the laryngeal cartilages 

 (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. 



