VERTEBRATA: AMPHIBIA. 515 



prior to birth, are furnished with vesicular external branchiae 

 placed on the side of the neck. In addition to the presence 

 of branchiae in the larva, the Caecilians are further connected 

 with the Amphibia by their possession of a double occipital 

 condyle and of a glandular skin ; whilst they approach the 

 Fishes in generally having small horny scales embedded in the 

 integument, and in the fact that the vertebrae are amphiccelous, 

 and the cavities formed by their apposition are filled with the 

 gelatinous remains of the notochord. As regards their distribu- 

 tion in space, the species of Ccecilia are found in India, Africa, 

 and South America; Siphonops and Rhinatrema are exclusively 

 American ; and Epicrium is exclusively Asiatic. 



ORDER II. URODELA ( = Ichthyomorpha, Owen; Sauroba- 

 trachia). This order is commonly spoken of collectively as 

 that of the " Tailed " Amphibians, from the fact that the larval 

 tail is always retained in the adult. The Urodela are charac- 

 terised by having the skin naked, and (except in Salamandra 

 ungniculata) destitute of any exoskeleton. The body is elongated 

 posteriorly to form a compressed or cylindrical tail, which is per- 

 manently retained throughout life. The dorsal vertebra are 

 biconcave (amphiccelous), or concave behind and convex in front 

 (opisthoccelous), and they have short ribs attached to the transverse 

 processes. The bones of the fore-arm (radius and ulna) on the 

 one hand, and those of the shank (tibia and fibula) on the other, 

 are not anchylosed to form single bones. 



In one section of the order formerly called Amphipneusta 

 the gills are retained throughout life, and the animal is there- 

 fore " perennibranchiate." In this section are the Proteus, 

 Siren, Menobranchus, &c. In the remaining members of the 

 order the gills disappear at maturity, and the animal is there- 



Fig. 279. Head and fore-part of the body of Proteus anguimis t showing the 

 external branchiae and tridactylous fore-limb. 



fore " caducibranchiate." In this section are the Land and 

 Water Salamanders. One form, however the Axolotl of 

 Mexico appears to be sometimes caducibranchiate, though 

 generally perennibranchiate. The genera Amphiuma and 

 Menopoma, also, exhibit a partially intermediate state of parts ; 



