222 FOSSIL ftEPTILES. 



brae. The ischium is nearly formed like the coracoid bones. 

 The femur is a little longer than the humerus. Its upper head 

 is compressed. It has but one trochanter, which is a pyra- 

 midal blunt eminence. The tibia approaches the usual form 

 in mammalia. Its upper head is gross and triangular. The 

 lower is crescentwise and placed obliquely, and its surface 

 is concave. The peroneum is slender and cylindrical. Nothing 

 in the calcaneum is worth remarking as different from what is 

 found in quadrupeds. But the figure of the astralagus, as in 

 all the lizards, is very singular and anomalous. The contour 

 of its anterior face is determined by four faces ; one upper, 

 which is small and square, for the peroneum ; one internal, for 

 the tibia, oblique, and elongated ; another is external, and 

 crescented, the upper and lower parts of which only bear against 

 the internal side of the peronean prominence of the calcaneum. 

 All the lower part of the astragalus is occupied by an irregular 

 surface, very convex, whose external posterior part rests in the 

 astragalian apophysis of the calcaneum, and the rest of which 

 supports the first two metatarsians. 



There are three bones more which must be reckoned among 

 those of the tarsus ; one analogous to the cuboid, placed between 

 the calcaneum and the last two metatarsians ; another, cunei- 

 form, which answers to the second and third metatarsian ; and 

 one supernumerary, flattened, triangular, with a point slightly 

 crooked, which is attached to the external side of the cuboid. 

 This holds the place of the fifth toe. 



A few words respecting the differences in the skeletons of 

 the caymans and gavials, from what we have now described, 

 will finish all we have to say respecting the living crocodiles. 



In the head of caymans, there are these differences from 

 that of the crocodiles. The anterior frontal, and the lachry- 

 mal, descend much less upon the muzzle. The holes pierced 

 on the upper face of the cranium, between the posterior 

 frontal, the parietal, and the mastoid bones, are much smaller, 

 and often disappear altogether, as in palpebrosus. A portion 



