472 



COMPAEATIVE ANATOMY. 



into two pieces. The arches are most numerous in the Chelonii, where 

 there are as many as three, and next to these come the Saurii; 

 in the Crocodilini the broad curved body of the hyoid has but a 

 single pair of arches. In the Ophidii the apparatus is reduced to a 

 cartilaginous remnant, and even these remnants of an arch are lost 



in various forms (Tortrix, Typhlops, etc.). 

 Two pairs of arches can be made out in Birds. 

 The rudimentary first arch fuses to form the 

 so-called entoglossal bone (Fig. 259, 2), pos- 

 teriorly to which lies the true body of the 

 hyoid. The second arch, however, is well 

 developed, and gives rise to the cornua (4 5), 

 which are formed of two large pieces, which 

 generally curve backwards behind the skull, 

 without being directly connected with it. Be- 

 hind the copula there is the remnant of a 

 second one, which forms the hyoid process (3). 

 In the Mammalia two arches are per- 

 manently connected with the single body of 

 the hyoid. The anterior cornua are the 

 largest, and are connected with the petrosal ; 

 they are made of several (three) pieces. When 

 the median piece is merely connected by a 

 ligament, this portion is divided in such a 

 way that the uppermost piece, if connected 

 with the petrosal, as it is in the Orang and in 

 Man, forms the styloid process of this bone ; 

 when this is the case, the remaining portion 

 is formed by the stylo-hyoid ligament, and the rest of the arch is 

 attached to the body of the hyoid as a small, and sometimes even 

 unossified piece. In most Mammals, the posterior cornua, which are 

 always formed of a single piece, are the smaller ; occasionally, as in 

 various Eodents and Edentates, they are altogether wanting. In 

 the Primates they are larger than the remnants of the anterior 

 cornua. They are connected with the larynx, the thyroid cartilage 

 of which is attached to them by ligaments. 



Fig. 259. Hyoid appara- 

 tus of the domestic fowl. 

 1 Body of the hyoid 

 (copula). 2 Entoglossal. 

 3 Hyoid process. 4 An- 

 terior, 5 Posterior por- 

 tion of the cornu of the 

 hyoid. 



Skeleton of the Appendages. 



§357. 



The two pairs of appendages in the Vertebrata, however much 

 they vary in the extent to which they are developed, have their 

 skeleton arranged in very much the same way ; this points to their 

 being homodynamous structures. In this skeleton we may dis- 

 tinguish an arched piece, which lies in the trunk, and which in its 

 lowest condition forms a band of cartilage ; according to the position 



