SAURIAN REPTILES. 317 



§ 4. Sauria. 



The conformation of those parts of the frame which are 

 subservient to progressive motion becomes more perfect in 

 the class of Saurian reptiles, which includes all the Lizard 

 tribes. Several links of connexion with the preceding class 

 may still be noticed, marking the progress of development, 

 as we follow the ascending series of animals. Rudiments 

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

 make their appearance very visibly in the Ophiosauriis, 

 and in the blind worm, {*Bnguis fragilis.) The Siren la- 

 certina has two diminutive fore feet, placed close to the 

 head. The Lacerta lumbricoides of Linnaeus, or the Bipes 

 canaliculatus of Lacepede, which is found in Mexico, and 

 of which a specimen is preserved 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 

 Lacerta bipes (Linn.) or Sheliopiisic of Pallas, has, on the 

 other hand, a pair of hind feet only, but extremely small, to- 

 gether with rudiments of a scapula and clavicle concealed 

 under the skin. Next in order must be placed the Chal- 

 cides, or Snake-lizard, (Fig. 210,) and the Lacerta seps, ani- 

 mals 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 pro- 

 gressive 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 degree of perfection. As a consequence 

 of this greater development of the skeleton, we find the 

 trunk divisible 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 between the lumbar and 

 the caudal vertebrae. 



