AJfTATOMY OF BATRAGHIANS. 467 



tinct Archegosaurus had in its larval life brancliial arches, 

 iind in fact so close are the affinities of some Amphibians to 

 tlie Ganoids that it is probable that both types have had a com- 

 mon origin ; while on the other liand the bones of certain 

 extinct scaly Labyrinthodonts have been regarded by some 

 •authors as reptilian; for exauiplc, the Carboniferous Mas- 

 todonsaurus v&s described as a reptile, but has been referred 

 to the Amphibians by modern writers. 



The sternum or breast-bone (Fig. 429, s) first appears in 

 the Batrachians. The shoulder-girdle is in great part carti- 

 Jaginous. In the toads and 

 frogs {Anura) the fore limbs, 

 "the radius, and ulna, and in 

 the hind limbs the tibia and 

 "fibula, grow together ; there 

 jire four toes in the fore feet, 

 jind five toes in the hind feet. 

 In the Siren the hind legs are yis.. 429.-steraum and shoulder-?; i-dio 



winfiiio- • in tlip pfintrn tinnk-pq °^ ^'°'^ (Bma lemporaria). p, body of 

 wanLing , in LUe COngO-SIiaKtS ,|,j, sternum ; so, scapula ; «', supra-frap- 

 ( 4m'nhiiimn\ +1ip limhc! nrp ula , co, coracoid-l) me, fused in ihe inil- 



■either t"wo or three-toed. ^'d,<^ W; '^'i '■]"^'<=J'' ; «. epistemnm Ti.e 



L'xlrerae shaded dunhle portion below p 

 The teeth of modern Ba- is thu xiphistcmam. The cirtilascinoua 

 . p.irts are shaded. —After Gegenbaur, 



trachians are conical or lobate, 



and microscopically are simple, "while those of the extinct 

 forms are mostly complicated by the labyrinthine infolding 

 ■of the "walls, as seen in microscojiic sections ; the teeth of 

 many Ganoids have a similir, though much simpler struc- 

 ture. 1'hey are usually of the same size, and may be ar- 

 ranged on projecting portions of different bones of the mouth, 

 i.e., the premaxillary, maxillary, mandibular, vomerine, pal- 

 atine, and pterygoid bones, as in fishes. In tadpoles and 

 in Sii^eji the jaw-bones are encased in liorny beaks like those 

 •of turtles and birds. In many Labyrinthodonts two tusks 

 were developed on the palate. The nasal canal is much as 

 ia the Dipnoan fish, the internal opening being situated in 

 the Perennibranchiates just within the soft margin of the 

 mouth. In the salHinaiiders and frogs it is bordered with 

 firmer parts of the jaw. The labyrinth of the ear is large, 

 and the tympanum or drum of the ear is external. Am- 



