466 



ZOOLOGY. 



Liibyriiithodonts such as Rhiachitomus, the vertebree are 

 ossified, but the centra consist of three j)ieces. In Cricotus 

 there are two kinds of bodies, centra and intercentra. The 

 ribs are rudimentary, exceijt in the bhud-worms (Cwcilia). 

 The skull is usually broad and flattened ; it differs from 

 that of fishes in having no bones representing the operculum, 

 suboperculum, interoperculum, or branchiostegal bones ; but 

 a memhraue bone probably homologous with the preojjercu- 

 lum is said to exist. (Cope.) The maxillary and premaxil- 

 lary bones are always present, usually armed with teeth ; no 

 Batraehian possesses a complete basioccipital, supraocci- 



pital, basisjihenoid, ali- 

 sphenoid, or jiresphe- 

 noid cartilage bone; 

 while "the frog's skull 

 is characterized by the 

 develojiment of a very 

 singular cartilage bone, 

 called by Cuvier the ' os- 

 en ceinttire,' or girdle- 

 bone."' (Huxley.) 



The embryonic carti- 

 lage persists in the low- 

 er jaw in adult Batra- 

 chians as in fishes, and 

 bony parts are developed 

 in connection with it 

 which essentially corre- 

 spond to those of fishes. 

 (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, i. e., 

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

 skulls of certain Labyrinthodonts are roofed in by broad, 

 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- 



Fig. 438.— Skeleton of a Prog, a, skull ; *, 

 vertebrse ; c, sacrum, and e, its continuation 

 (ui-ostyle); /, suprascapula ; g, liumcrus ; //, fore- 

 arm bones ; «, wrist bones' (carpals and meta- 

 carpals) ; rf, ilium ; m, thit^h ^l■emur) ; ?;, leg 

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

 bones (tarsals) ; p, q, foot bones or phalanges. 

 — After Owen. 



