28 THE ANATOMY OF "VERTEBEATED ANIMALS. 



directly with the skull in mammals, but only indirectly, or 

 through the intermediation of the quadrate, in other Verte- 

 hrata. In birds and reptiles, the proximal end of the 

 quadrate bone, articulates directly (with a merely apparent 

 exception in Ophidia), and independently of the hyoidean 

 apparatus, with the periotic capsule. In most, if not all 

 fishes, the connection of the mandibular arch with the skull 

 is effected indirectly, by its attachment to a single cartilage 

 or bone, the hyomandibular, which represents the proximal 

 end of the hyoidean arch (see Fig. 24). 



The ossification of the hyoidean apparatus varies im- 

 mensely in detail, but usually gives rise to bony lateral 

 arches, and a median poi'tion, bearing much the same rela- 

 tion to them as the sternum has to the ribs. When the 

 lateral arches are complete they are connected directly with 

 the periotic capsule. 



The proximal end of the hyoidean arch is often united, 

 more or less closely, with the outer extremity of the bone, 

 called columella auris, or stapes, the inner end of which, 

 in the higher Vertebrata, is attached to the membrane of the 

 fenestra ovalis. 



In ordinary fishes, a fold of the integument extends 

 backwards from the second visceral arch over the per- 

 sistent branchial clefts; within this is developed a series 

 of raylike membrane bones, termed opercular and bran- 

 chiostegal, which become closely connected with the hyoidean 

 arch. A corresponding process of the skin is developed in 

 the Batrachian Tadpole, and grows backwards over the 

 branchiae. Its posterior edge, at first free, eventually unites 

 with the integument of the body, behind the branchial clefts, 

 the union being completed much earlier on the right side, 

 than on the left. 



In most mammals a similar fold of integument gives 

 rise to the pinna, or external ear. 



The branchial skeleton bears the same relation to the 

 posterior visceral arches that the hyoidean does to the 

 second. When fully developed, it exhibits ossified lateral 

 arches, connected by median pieces, and, frequently, pro- 



