24 FOSSIL REPTILIA OF THE LONDON CLAY. 



as the appendage of the scapular arch modified and developed for a similar office, 

 a close resemblance is maintained in the subdivisions of the framework of both limbs. 

 The first bone of the pelvic limb, called the ' femur/ is longer than the humerus, and, 

 like it, presents an enlargement of both extremities, with a double curvature of the 

 intervening shaft, but the directions are the reverse of those of the humerus, as may be 

 seen in T. XI, where the upper or proximal half of the femur is concave, and the distal 

 half convex, anteriorly. The head of the femur is compressed from side to side, not 

 from before backwards as in the humerus ; a pyramidal protuberance from the inner 

 surface of its upper fourth represents a ' trochanter ;' the distal end is expanded 

 transversely, and divided at its back part into two condyles. 



The next segment or ' leg,' includes, like the corresponding segment of theforelimb 

 called ' forearm,' two bones. The largest of these is the ' tibia,' and answers to the 

 radius. It presents a large, triangular head to the femur ; it terminates below by an 

 oblique crescent with a convex surface. 



The ' fibula' is much compressed above ; its shaft is slender and cylindrical, its 

 lower end is enlarged and triangular. 



All these long bones have a narrow medullary cavity. 



The group of small bones which succeed those of the leg, are the tarsals ; they are 

 four in number, and have each a special name. The ' astragalus' articulates with the 

 tibia, and supports the first and part of the second toe. It is figured in Cuvier's 

 'Ossemens Fossiles,' torn, v, pt. ii, pi. iv, figs. 19 A, B, C, D. The 'calcaneum' inter- 

 venes between the fibula and the ossicle supporting the two outer toes ; it has a short 

 but strong posterior tuberosity. 



The ossicle referred to represents the bone called ' cuboid' in the human tarsus. 

 A smaller ossicle, wedged between the astragalus and the metatarsals of the second 

 and third toes is the ' ectocuneiform.' 



Four toes only are normally developed in the hind-foot of the Crocodilia ; the fifth 

 is represented by a stunted rudiment of its metatarsal, which is articulated to the 

 cuboid and to the base of the fourth metatarsal. 



The four normal metatarsals are much longer than the corresponding metacarpals. 

 That of the first or innermost toe is the shortest and strongest ; it supports two 

 phalanges. The other three metatarsals are of nearly equal length, but progressively 

 diminish in thickness from the second to the fourth. The second metatarsal supports 

 three phalanges ; the third four ; and the fourth also has four phalanges, but does 

 not support a claw. The fifth digit is represented by a rudiment of its metatarsal in 

 the form of a flattened triangular plate of bone, attached to the outer side of the 

 cuboid, and slightly curved at its pointed and prominent end. 



In the skull of the Crocodile, as of most other vertebrates, there are intercalated 

 a few bones, or ossified parts of special organs, which, as is shown in the classed 

 Table of the bones of the head, do not belong to the vertebral system of bones. 



