466 



ZOOLOGY. 



Labyrinthodonts such as Rhiachitomus, the vertebra are 

 ossified, but the centra consist of three pieces. In Cricotii* 

 there are two kinds of bodies, ci'iitra and i/tfrrccii />//. Tlie 

 ribs are rudimentary, except in the blind-worms (>',,;!! ia}. 

 The skull is usually broad and flattened : it differs from 

 that of fisbesir. having no bones representing the opeiculum, 

 subopereulum, interoperculum, or branchiostegal bones ; but 

 a membrane bone probably homologous with the preopercu- 

 Inm is said to exist. The maxillary are usually and the prc- 

 maxillary bones always present, usually armed with teeth : no 

 Batrachian possesses a complete basioccipital, snpraocci- 



pital, basisphenoid, ali- 

 sphenoid, or presphe- 

 noid cartilage bone; 

 while "the frog's skull 

 is characterized by the 

 development of a very 

 singular cartilage bone, 

 called by Cuvier the ' os- 

 en ceinture,' or girdle- 

 bone.'' (Iluxle}'.) 



The embryonic carti- 

 lage persists in the low- 

 er jaw in adidt Batra- 

 chians as in fishes, and 

 Fig. 428 Skeleton of a Frog. , skuii ; b, bony parts are developed 



vertebrae ; c, sacrum, and e, its continuation , > . ... 



(iirostyle);/, Huprascapala; y, humerns; A, fore- m connection AVltll it 

 ami bones'; i, wrist bones (carpals and meta- _ . . . .. 



carpals) ; d, ilium ; m, thigh (femur) ; , ] e g which essentially COl're- 

 bone (ulna) : o, elongated first pair of ankle- , , , ',, fi , 



boiu-s (taisals) ; p, q, foot bones or phalanges. Spoiltl tO tllOSe OI HSlieS. 



(Gegenbaur.) 



The suspensorium is immovably joined to the skull, and 

 with it is connected the hyoidean arch. The branchial 

 arches in the tailed forms persist in varying numbers, /. e., 

 from two to four, but are dropped in the toads and frogs. The 

 skulls of certain Labyrinthodonts are roofed in by hroad. 

 flat bones, so that they bear a strong resemblance to certain 

 Ganoids represented by the garpike, while Gegenbaur states 

 that there are many bony parts in the skull of the Batra- 

 chians which resemble those in the Dipnoan fishes. The ex- 



