XIII 



PHYLUM CHORDATA 287 



hand and the shank and foot extending backwards and downwards. 

 Each limb thus presents an external or dorsal and an internal 

 or ventral surface, an anterior or pre-axial border which terminates 

 in the first digit, and a posterior or post-axial border which ter- 

 minates in the last digit. The eyes are small and have no eyelids, 

 there is no tympanic membrane, and the mouth is wide and bor- 

 dered by thick lips. On each side of the neck are two gill-slits 

 (br. cl. 1, br. d. 2) leading into the pharynx, the first between the 

 first and second branchial arches, the other between the second 

 and^third. From the dorsal end of each of the three branchial 



FIG. 955. Salamandra maculosa. (After Cuvier.) 



arches springs a branched external gill (br. 1 br. 3). Very 

 similar in its external characters is the blind, cave- 

 dwelling Proteus ; and Siren (Fig. 953) differs mainly in 

 its elongated eel-like body and in the absence of hind- 

 limbs. All three genera are perennibranchiate or persistent- 

 gilled. 



The remaining Urodela are often called caducibranchiate 

 or deciduous-gilled, and furnish a complete series of 

 transitions from derotrematous forms which, while losing 

 the gills, retain the gill-clefts, to salamandrine forms in 

 which all trace of branchiate organisation disappears in the adult. 

 In Amphiuma (Fig. 954) the body is eel-like and the limbs are ex- 

 tremely small : there are no gills in the adult, but two pairs of gill- 

 openings are retained throughout life. In Cryptobranchus there is a 

 single branchial aperture, sometimes present on the left side only ; 

 but, as in the previously mentioned genera, four branchial arches 

 are retained. In Megalobatrachus, the Giant Salamander of Japan 

 and China, all trace of gill-slits disappears, but two branchial arches 

 persist. Lastly, in the Salamanders, such as the spotted Salamander 

 (Salamandra maculosa, Fig. 955) of Europe, and the common British 

 Newts (Molge), the adult has no trace either of gills or gill-slits, 



