IV. VERTEBRATA: AMPHIBIA. 



513 



MONOPNEUMONIA, with One swim bladder: Ceratodus, Australia. Dipneu- 

 MONIA, witli two bladders: Proloptenis, Africa; Lepidosiren, South America. 

 The larvas of both have four pairs of gills, three of which are retained in Protop- 

 lenis. Possibly the paleozoic Arthrodira, some of gigantic size (Diniclithys), 

 belong here. 



Class III. Amphibia. 



There are two views as to the origin of the Amphibia. According to 

 one they have descended from Crossopterygian 

 ganoids; the other is that they have come from 

 the Dipnoi. The class is distinguished at once 

 from the fishes by the absence of fins. There is, 

 it is true, a median fin in larval life, and this 

 may persist (Perenniljranchs, Triton), but it is 

 never divided into dorsal, caudal, and anal, 

 and it lacks any skeletal support (figs. 4, 5). 

 The paired fins are replaced by toed feet (p. 

 464). These are often webbed and are used 

 for swimming, for creeping and leaping, and are 

 consequently jointed between the separate skele- 

 tal elements (fig. 564). Besides the shoulder and 

 hip joints, which alone occur in fishes, there occur 

 also elbow (knee), wrist (ankle), and finger 

 joints. The number of digits is not always five, 

 for a reduction to four, three, or even two occurs. 



The connexion of the girdles with parts of the 

 axialeskeleton (lacking in most fishes) is of impor- 

 tance. The pelvic girdle is connected with the 

 vertebral column by means of the ilium, which 

 arti ulates either directly or by a sacral rib with 

 the single sacral vertebra. Ventrally the two 

 halves of the girdle fuse, and usually the limits 

 of ischium and pubis cannot be traced. 



The attachment of the pectoral girdle is less 

 firm (fig. 521, A). The dorsal portion, the scap- 

 ula, ends free in the muscles; the ventral, differ- 

 entiated into coracoid and clavicle, either meets the opposite side in a 

 symphysis {firmislernous Anura) or the two sides overlap {arciferous Anura 

 and urodeles). A connexion with the vertebral column does not exist 

 since the sternum (lacking in urodeles) is not connected with the ribs. 

 The sternum extends forward to the clavicle and coracoid, and in the 

 firmisterna is continued forward by an epistenmm (fig. 521, A). 



33 



Fig. 564. — Skeleton of 

 hind leg of Salamandra 

 maculosa larva (from 

 Gegenbaur). c, centrale; 

 F, fibula; /, fibulare; i<'g, 

 femur; i, intermedium; T, 

 tibia; t, tibiale; 1-5, car- 

 palia and corresponding 

 metacarpals and digits. 



