5 I2 



MANUAL OF ZOOLOGY. 



phosis takes place, this is completed before the young animal 

 begins to lead a free existence. 



The endoskeleton of the Amphibia is generally well ossified, 



Fig. 277. Tailed Amphibians. A, Siren lacertina ; B, Ainphiuma, showing the four 

 minute limbs ; C, Menobranchtis maculatus. (After Mivart.) 



and the skull possesses two occipital condyles. The vertebrae 

 are biconcave or amphiccelous (as in Fishes) in Proteus, Caril- 

 ians y and most of the extinct Labyrinthodonts. In the Sala- 

 manders and Surinam Toads the vertebrae are opisthocoelous, 

 but most of the other Amphibians have procoelous vertebrae. 

 The length of the vertebral column is greatly reduced in the 

 tail-less forms, and the number of vertebrae is correspondingly 

 small. The sacrum is seldom composed of more than one 

 vertebra, and there are often no separately-ossified ribs. In the 

 Tailed Amphibians and the Caecilians, however, there are well- 

 developed ribs, which are never supplemented in front by 

 sternal ribs, though a cartilaginous or partially-ossified sternum 

 may be present. 



Limbs may be entirely wanting (as in the Caecilians and 

 some of the Labyrinthodonts) ; but all the other members of 

 the class possess both pairs of limbs, with the exception of the 

 genus Siren, in which the pelvic limbs are wanting (fig. 277). 



The skin is mostly soft, moist, and richly provided with 

 glands ; the Caecilians have mostly small rounded horny 

 scales imbedded in the integument; and the extinct Laby- 



