CROCODILIA. 23 



scapula, which margin is morticed into a groove at the anterior border of the broad 

 rhomboidal cartilage continued beyond the ossified part of the manubrium, which forms 

 the key-bone of the scapular arch. The anterior locomotive extremity is the 

 diverging appendage of the arch, under one of its numerous modes and grades of 

 development.* 



The proximal element of this appendage or that nearest the arch, is called the 

 'humerus' (53, fig. 9) : its head is subcompressed and convex; its shaft bent in two 

 directions, with a deltoid crest developed from its upper and fore part ; its distal end 

 is transversely extended, and divided anteriorly into two condyles. The shaft of 

 this bone has a medullary cavity, but relatively smaller than in the mammalian 

 humerus. 



The second segment of the limb consists of two bones : the larger one (54) is called 

 the ' ulna :' it articulates with the outer condyle of the humerus by an oval facet, the 

 thick convex border of which swells a little out behind, and forms a kind of rudimental 

 ' olecranon ;' the shaft of the ulna is compressed transversely, and curves slightly out- 

 wards ; the distal end is much less than the proximal one, and is most produced at the 

 radial side. 



The radius (55) has an oval head; its shaft is cylindrical; its distal end oblong and 

 subcompressed. 



The small bones (56) which intervene between these and the row of five longer 

 bones, are called ' carpals :' they are four in number in the Crocodilia. One seems to 

 be a continuation of the radius, another of the ulna ; these two are the principal 

 carpals ; they are compressed in the middle and expanded at their two extremities ; 

 that on the radial side of the wrist is the largest. A third small ossicle projects 

 slightly backwards from the proximal end of the ulnar metacarpal : it answers to the 

 bone called ' pisiforme' in the human wrist. The fourth ossicle is interposed between 

 the ulnar carpal and the metacarpals of the three ulnar digits. 



These five terminal jointed rays of the appendage are counted from the radial to 

 the ulnar side, and have received special names : the first is called ' pollex,' the second 

 c index,' the third ' medius,' the fourth ' annularis,' and the fifth ' minimus.' The first 

 joint of each digit is called ' metacarpal ;' the others are termed ' phalanx.' In the 

 Crocodilia the pollex has two phalanges, the index three, the medius four, the annularis 

 four, and the minimus three. The terminal phalanges, which are modified to support 

 claws, are called ' ungual' phalanges. 



As the above-described bones of the scapular extremity are developments of the 

 appendage of the scapular arch, which is the haemal arch of the occipital vertebra, it 

 follows, that, like the branchiostegal rays and opercular bones in fishes, they are 

 essentially bones of the head. 



The diverging appendage of the pelvic arch being a repetition of the same element 



* See my Discourse ' On the Nature of Limbs,' 8vo, Van Voorst, 1849, pp. 64-70. 



