IchtTiyosauria. 



Wall-case, 

 No. 14. 



Table-cases, 

 Nos. 4, 5. 



two centralia in the carpus of these higher forms is therefore an 

 acquired and not an inherited character. 



The structure of the palate is essentially the same as in 

 Sphenodon. There is a remarkable resemblance between the 

 Ichthyopterygia and the Rhynchocephalia in the structure of 

 the pectoral arch, in the presence in both of abdominal ribs ; in 

 the similar position of the parietal foramen in the cranium, and 

 the relation of the quadratojugal to the surrounding bones. In 

 both there is the same absence of a lateral vacuity in the 

 mandible. 



FIG. 45. (A) Ventral aspect of the left pectoral limb of Ichthyosaurus Cto?i?/&ean(Lydekker) ; 

 Lower Lias, Lyme Regis ($ nat. size). 7i, humerus ; r, radius ; u, ulna ; i, inter- 

 medium. The vertical lines show the relative lengths of the limb and the skull, the 

 longer line being that of the skull. The notches in the anterior border of the first 

 row of phalangeals are omitted. (B) Dorsal aspect of the left pectoral limb of 

 Ichthyosaurus communis (Conybeare) ; Lower Lias, Lyme Regis. The letters and lines 

 are the same as in Fig. A. 



The teeth are confined to the jaws and are implanted in a 

 continuous groove, without anchylosis of the bone. Their crowns 

 are sharply pointed, and they are usually cylindrical and deeply 

 fluted, more rarely carinated, compressed, or smooth (see Fig. 

 44 A, B, o). 



