CHAPTER VIII 



LACERTA : A CHORDATE LIVING ENTIRELY ON LAND 



Externals. — In general shape, the lizard is not very dissimilar 

 from the newt, but it differs from it in one very important 

 respect, which is characteristic of all the animals (Reptiles) of 

 the group to which the lizard belongs. The body is covered 

 with scales formed from the epidermis, and therefore totally 

 different from the true scales of fish, which are always formed 

 from the (mesodermal) dermis. To mark this distinction, 

 the scales of reptiles are called corneoscutes. They cover the 

 whole body including the limbs and head, and on the latter 

 their arrangement does not correspond with that of the under- 

 lying bones. On the last phalanges of the fingers and toes, 

 the scales form horny claws. Underlying the corneoscutes 

 of the head there are ossifications of the dermis forming osteo- 

 scutes, which fuse with the underlying bones of the skull. 



The skin is dry and devoid of glands. The eyes have upper 

 and lower eyelids, and also a so-called " third eyelid " or nicti- 

 tating membrane. Behind the eye is a circular area sunk 

 slightly below the level of the skin, and covered over like a 

 drum by the tympanic membrane or ear-drum. The external 

 nostrils are on the side of the snout ibove the mouth. At the 

 base of the tail is the cloaca, which in the male is provided 

 with a pair of protrusible copulatory organs. 



Skull. — The skull of the lizard, although well ossified, 

 has several holes in it, separating the membrane-bones. The 

 nasal aperture is bounded by the premaxilla, nasal and maxilla. 

 The orbit is limited by the prefrontal, frontal, and postfrontal 

 above, and the lachrymal, jugal, and postorbital beneath. 

 Behind the orbit is an aperture called a temporal fossa, in 



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