CRETACEOUS FORMATIONS. 53 



nearly straight, and become gradually wider and thicker towards the end attached to 

 the sacrum : of these bones a portion 25 inches long is preserved of the one, (T. XII, 

 fig. 6,) and 20 inches of the other : the broadest end of the longer portion measures 

 across 10 inches. In a second block, the mesial extremities of the pubis and ischium 

 are preserved. The exposed surface of the pubis is principally convex, but becomes 

 concave towards the opposite or median margin : it measures across at its broadest 

 part 13 inches; the length of the fragment preserved is 17 inches. The diameter 

 of the corresponding expanded extremity of the ischium is 9 inches : its expanded 

 extremity is obliquely truncated ; that of the pubis is rounded. In another block the 

 expanded extremity of the opposite pubis is preserved ; it measures 14 inches across, 

 and is 22 inches in length. 



In a third large mass of rock, the fragment of an enormous, apparently sub- 

 quadrilateral flat bone, is exhibited, which most probably belongs to the pectoral arch, 

 and, in that case, must be the coracoid bone, T. XII, fig. 5, p. The length of this 

 fragment is two feet, its greatest breadth 1 7 inches : its thickness varies from 3 to 

 5 inches. On one side there is a slight submedian ridge, from which the surface 

 slopes away with a gentle concavity. 



The breadth of this bone indicates the great development of the muscles destined 

 for the movement of the fore-leg, whence it may be inferred that the anterior 

 extremities were more powerfully and habitually used in progressive motion than in 

 the Crocodiles. In the existing species of this family, the anterior extremities are 

 used chiefly for the support and movements of the body on land ; they are applied to 

 the sides of the chest when the animal swims, which is chiefly effected by the actions 

 of the strong and long vertically compressed tail. The lateral movements of the fore- 

 legs being much restricted, the coracoid bone and the muscles arising from it are 

 comparatively slender. In the Enaliosauria, where the fore-legs are converted into 

 paddles for swimming, the coracoids are vastly expanded, both for the increased 

 strength of the shoulder-joint and the increased surface for the attachment of the 

 muscles, which effect the lateral movements and the stroke of the paddle-shaped limb 

 upon the water. We may infer, therefore, that the anterior extremities of the present 

 gigantic Crocodilian were, by some webbed modification of the hand, better adapted, 

 and more energetically used for swimming than in the existing Crocodilians. 



The shaft of a long bone somewhat similar to, but shorter and more slender than 

 the femur, and crushed, is preserved with that of a smaller bone, tapering more 

 gradually to one end, in the same block of stone : these are figured in T. XIII, fig. 2 ; 

 the larger bone is probably the humerus, h, the smaller one the ulna, u. 



Other less intelligible fragments of the long bones of the same great Saurian are 

 represented in T. XII, figs. 2, 3, and 4 ; and in T. XIII, figs. 2 and 4. Fig. 3 probably 

 shows two of the metacarpals in the same block of stone. 



The principal parts above described are preserved in the British Museum, to 



