XIII 



PHYLUM CHORDATA 



293 



pollex being the smallest. The hind-limbs arise from the posterior 

 end of the trunk towards the ventral aspect ; each, like that of the 

 Frog, consists of three divisions thigh or femur, shank or cms, 

 and foot or pcs. The pes, like the manus, terminates in five 

 clawed digits, of which the first or hallux is the smallest. The 

 head is somewhat pyramidal, slightly depressed : the openings of 

 the external nares are situated above the anterior extremity. The 

 mouth is a wide slit-like aperture running round the anterior 

 border of the head. At the sides are the eyes, each provided with 

 upper and lower opaque movable eyelids and with a transparent 

 third eyelid or nictitating membrane, which, when withdrawn, lies 



FIG. 903. Lacerta viridis. (After Brelini.) 



in the anterior angle of the orbit. Behind the eye is a circular 

 brown patch of skin the tympanic membrane corresponding 

 closely to that of the Frog, but somewhat sunk below the general 

 level of the skin. The trunk is elongated, strongly convex 

 dorsally, flatter at the sides and ventrally. At the root of the 

 tail on the ventral surface is a slit-like transverse aperture the 

 anus or cloacal aperture. The tail is cylindrical, thick in front, 

 gradually tapering to a narrow posterior extremity ; it is nearly 

 twice as long as the head and trunk together. 



There is an exoskeleton of horny epidermal scales covering 

 all parts. In size these differ in different positions. On the dorsa 



