BRAJfCHlAL SKELETON OF VERTEBRATA. 



471 



Fig. 257. Hyoid, and brau- 

 cliial arches of a larva of 

 Salamandra maculosa. 

 h Hyoid arch, c c Supports 

 of the branchial arches. 

 d Appendage of the Copula. 



Fig. 258. Hyoid of Bufo 

 cincreus. n Copula, i Cor- 

 nua of the hyoid. c Eeui- 

 nants of the branchial 

 arches (after Duges). 



present at tlie same a gradual change in this apparatus. It is 

 retained in the Perennibranchiata, and undergoes slight changes 

 only in the Derotremata. It is made up of four or five pairs of 

 arches ; the first of which, as in Fishes, forms a hyoid arch (Fig. 

 257,6). The suc- 

 ceeding arches are 

 united to a com- 

 mon copula. The 

 posterior ones do 

 not severally ex- 

 tend as far as it, 

 hut are connected 

 together on either 

 side. In correlation 

 with the reduction 

 of the arches, the co- 

 pulas are increased 

 in size. The only 

 portion which re- 

 mains complete 

 after metamorpho- 

 sis is the hyoid (Fig. 258, h). It is united with the copula {a), 

 which is generally of some size, and which is converted into_ the 

 body of the hyoid. A larger piece of the second arch is retained 

 in the Salamandrina, and a small portion of the third arch ; in the 

 Anura, however, there is a cartilaginous plate, which is made up 

 of all the branchial arches on either side, and which fuses with 

 the copula into one piece. Eod-shaped pieces (columellee), which 

 are developed from the ends of the primitively paired plates, are 

 attached to this (Fig. 258, c). 



The changes in the branchial skeleton, which are perceptible 

 when it changes its function, afford a striking example of the great 

 influence which adaptation to external conditions of life exercises on 

 the internal organisation. 



§ 356. 



The degeneration which is seen in individuals among some of the 

 Amphibia is an inherited arrangement in the higher classes. Except 

 those parts which enter into the composition of the auditory organ, 

 all the parts which were developed at one time from the large 

 branchial skeleton of Fishes, are converted into that support for the 

 tongue, which is known as the hyoid bone. The copula forms its 

 " body," and to this the rest of the arches are attached, under the 

 form of " cornua." As a rule the remains of two arches — the hyoid 

 portion of the primitive hyoid, and parts of the first branchial arch 

 — are used for this purpose. 



The simple body, which rarely consists of several pieces, is 

 beset, in Eeptiles, with portions of two or three arches ; these 

 are often very rudimentary. They are either single, or divided 



