ANATOMY OF VERTEBRATES. 



57 



48 



from the 32 anterior ones, directed backward in the first ten, and 

 forward in the last ten, where they are unusually long, and tipped 

 with a coat of hard dentine ; these perforate the cesophagus, and 

 serve as teeth. The jaws are merely roughened by rudiments of 

 teeth. The relation of this singular condition of the cervical 

 hypapophyses and the modification of the dental system to the 

 food of the Deirodon will be explained in the chapter on teeth. 



§ 22. Vertebral column of Lacertia. — The anguine or snake- 

 like reptiles, with fixed upper-jaws and a 

 scapular arch, pass gradually, by other forms 

 with rudiments of limbs (Pseudojms), to the 

 slender-bodied long-tailed lacertians. The dis- 

 tinction is effected through the establishment 

 of a costal arch in the trunk, completed by the 

 addition of a hasmal spine (sternum) and hasma- 

 pophyses (sternal ribs) to the pleurapophyses 

 or vertebral ribs, which are alone ossified in 

 Ophidia. 



The vertebras of the trunk have the same procoslian character, 

 i. e., with the cup anterior and the ball behind, fig. 48 ; the latter, 

 c, being usually less prominent, more oblique, and more trans- 

 versely oval than in serpents. The vertebras also are commonly 

 larger, and always fewer in number than in the typical Ophidia. 



Those of the Iguanas retain the superadded articular surfaces 

 of the zygosphene, fig. 48, zs, and zygantrum ; but I have not 

 met with these superadded processes in other lacertians. In the 



Trunk vertebra, Iguana 



49 



Fore part of skeleton of a Lizard 



Geckos the vertebras are, exceptionally, biconcave. * The ribs do 

 not begin to be developed so near the head as in Ophidia. Not 

 only the atlas and dentata, but the third vertebra, fig. 49, and 

 sometimes, as in the Monitor ( Varanus), the four following verte- 

 bras, are devoid of pleurapophyses : when these first appear they 



1 Sec those of the subgenus Ithynchoceplialus, xliv. vol. i. No. 662, p. 142. 



