FOSSIL REPTILES. 295 



crocodiles. In different tortoises it varies in formation. In 

 the lizards it presents some analogies with that of birds, but its 

 composition is more complex. To enter, however, into all its 

 variations in this great family is not necessary here. It will be 

 sufficient to observe, that it has, in general, a simple body^ and 

 two pair of cornua, and sometimes even a third. From the 

 body in front is a process like a thin stem, which is more or 

 less prolonged in a cartilage^ which penetrates into the tongue. 

 The anterior cornua are variously folded, and the posterior 

 variously directed, according to the species. Those of the third 

 pair are not very often found, and when they do exist may be 

 considered rather as posterior processes of the body of the 

 bone, than particular cornua. 



We must now give some attention to the vertebrae and ribs 

 of the lizards, as they are of such importance in the determi- 

 nation of the fossil remains of this immense family. 



The atlas of the monitor is a ring composed of three pieces ; 

 two upper ones emarginated, in front and back for the nerves, 

 and united to each other at the dorsal part, and one lower 

 piece. 



The piece of the axis analogous to the odontoi's penetrates 

 into the ring of the atlas, and fills nearly half its breadth, 

 leaving, however, in front, a concavity for the condyle of the 

 head. A triangular piece, underneath, on the junction of the 

 atlas, the odontoid, and the axis, forms a sort of pointed crotchet 

 directed backwards. 



The axis is compressed, and its annular part above is formed 

 like a sharp longitudinal crest. Its anterior articulary facets 

 are turned outwards, the posterior downwards. The body is 

 terminated in a transverse convexity, of the form of a kidney. 

 At each of its lateral faces is a small crest, not projecting much, 

 with a small point towards the third part of its front. Under- 

 neath, is a crest, under the lower part of the bone, which 

 widens behind. 



The succeeding five vertebrae resemble the axis, but have no 



