REPTILES 1391 



bones of the extremities, and, also, of the sternum, 

 make their appearance very visibly in the Ophiosau- 

 rus, and in the blind-worm (Anguis fragilis). The 

 Siren lacertina has two diminutive forefeet, placed 

 close to the head. The Lacerta lumbricoides of Lin- 

 naeus, or the Bipes canaliculatus of Lacepede, which 

 is found in Mexico, and of which a specimen is pre- 

 served in the collection at Paris, has a pair of very 

 short feet, also placed near the head, and divided 

 into four toes, with the rudiment of a fifth. The La- 

 certa bipes (Linn.), or Sheltopusic of Pallas, has, on 

 the other hand, a pair of hindfeet only, but ex- 

 tremely small, together with rudiments of a scapula 

 and clavicle concealed under the skin. Next in order 

 must be placed the Chalcides, or snake-lizard, and 

 the Lacerta seps, animals frequently met with in the 

 south of France, and which have four minute feet, 

 totally inefficient for the support of the body, and 

 only remotely useful in contributing to its progres- 

 sive undulations. 



Ascending from these, we may form a series of 

 reptiles, in which the development of the limbs 

 becomes more and more extended, till we arrive at' 

 crocodiles, in which they attain a considerable de- 

 gree of perfection. As a consequence of this greater 

 development of the skeleton, we find the trunk divisi- 

 ble into separate regions. We now, for the first time, 

 meet with a distinct neck, separating the head from 

 the thorax, which is itself distinguishable from the 

 abdomen ; and a distinct sacrum is interposed be- 

 tween the lumbar and the caudal vertebrae. 



The number of ribs differs in different species of 



