THE BONES IN THE ENALIOSAURIA. 325 



The palate of lizards diflPers in not being entirely closed me- 

 sially, in the totally different condition of the posterior nares, 

 in the small size of the transverse bone, in the teeth on the ptery- 

 goid bone &c., and by the pterygoid bones not meeting to cover 

 the basisphenoid. The occipital condyle is made to a leas extent 

 in lizards by the basioccipital bone than in Plesiosaurs. 



The Plesiosaurian lower jaw has not the prominent coronoid 

 process or the inward extension of the articular bone of 

 Lizards. 



The vertebral column of lizards like the Monitor includes as 

 many vertebrae as in Plesiosauriis ; only, instead of being chiefly in 

 the neck and tail, they are chiefly in the tail, and the neck has 

 only about half a dozen. 



In Monitor and all lizards except the Gecko the centrum dif- 

 fers in its elongation and procoelous articulation. [The skeleton 

 of a Gecko I have not seen.] The cervical vertebrse moreover 

 differ in often having a strong hypapophysis. The dorsal vertebrae 

 differ in the lateral extension of the zygapophyses, the absence of 

 transverse processes, aud the articulation of the ribs to the side 

 of the centrum. The caudal vertebrae differ in having the chevron 

 bones attached to the base of the centrum or its posterior margin, 

 though there are a few Plesiosaurs (of undescribed species) in 

 which this character is seen. The dorsal ribs of lizards are very 

 like those of Plesiosaiirus ; but no lizard has similar abdominal 

 ribs. 



Neitter pectoral nor pelvic arches have much in common with 

 Plesiosaurus . In order to make the pectoral arch like that of a 

 Plesiosaur, it would be necessary to blend the clavicles and inter- 

 clavicle and contract the triradiate limbs of the latter bone till the 

 scapulae were nearly drawn together anteriorly, and the acromion 

 became a terminal process at the free end of the bone. Then, by 

 suppressing the sternum, the coracoid bones would come together 

 mesially, and it would only be necessary to make a continuous 

 ossification over the interspaces of the coracoid to have a pelvic 

 arch essentially that of a Plesiosaurian. 



In the same way, by expanding the lizard-pubis on its anterior 

 border to a convex outline which should make the bone reniform 

 and lie in one plane, and by then drawing the bone back to 

 meet the ischium at the symphysis and rounding off the angles 

 and ridges of the ilium, the pelvic arch would approach the ple- 

 siosaurian type. 



