AMPHIBIANS 245 



been described for the Sand Lizard (see p. 191). The provision 

 for renewal of air in the lungs is, however, different, for there 

 is here no means of altering the capacity of the chest by move- 

 ments of ribs and sternum, air being in this case renewed in 

 the lungs by the upward and downward movement of the floor 

 of the mouth-cavity. During this process the mouth is kept 

 shut, air passing from and to the exterior through the nose, 

 which opens externally by valvular nostrils and internally by 

 small apertures on the roof of the mouth. 



The Salamander, too, is not altogether dependent on the 

 lungs for the purification of its blood, as the moist skin also 

 serves as an accessory breathing-organ, the blood which it purifies 

 entering the great veins which pour impure blood into the sinus 

 venosus. This blood is therefore less impure than would otherwise 

 be the case. 



The brain (fig. 150) is much like that of the Sand Lizard, 

 but is of lower type, it being especially noticeable that both 

 cerebral hemispheres and cerebellum are smaller in proportion. 

 As regards the chief sense organs, the eye is not provided with 

 a, third eyelid, and its crystalline lens is spheroidal instead of 

 being biconvex as in animals better adapted for a terrestrial 

 life. The ear on each side consists essentially of a membranous 

 labyrinth not unlike that found in a Lizard (see p. 203). There 

 are, however, no special arrangements, for conducting sound- 

 waves. This, however, is not a feature which characterizes all 

 Amphibia; the frog, for example, having a tympanic cavity and 

 tympanic membrane, and a small rod, the columella or ear-bone, 

 running from that membrane to the part of the skull in which 

 the membranous labyrinth is lodged. 



The Amphibia now living are divided into three orders: — 

 I. Urodela, or Tailed Amphibia; 2. Anura, or Tailless Amphibia; 

 and 3. Gymnophiona, or Limbless Amphibia. 



Order i. — Tailed Amphibians (Urodela) 



Salamanders, Newts, and allied forms are here included 

 (fig. 152). The Spotted Salamander {Salamandra maculosa), 

 just described, is a good example of the Urodela. Its relative, 

 the Black Salamander {S. atra), is a smaller Alpine form, and 

 other allied species inhabit the Peninsula and the Caucasus. 



