CROCODILIA. 103 



thick convex border of which swells a Httie 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 (sG) 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 ' poUex,' the second 

 ' 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 poUex 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. 



But the enumeration of the bones of the crocodile's skull is not completed by these: 

 there is a bone anterior to the orbit, marked 73 in fig. 13, and in PI. 1 A and J2 ; it is 

 perforated at its orbital border by the duct of the lachrymal gland, whence it is termed 

 the 'lachrymal bone,' and its facial part extends forwards between the bones marked 

 14, 15, 21, and 26. In many Crocodilia there is a bone at the upper border of the 

 orbit, which extends into the substance of the upper eyelid ; it is called ' superorbital.' 

 In the Crocodllm palpehrosus there are two of these ossicles. 



Both the lachrymal and superorbital bones answer to a series of bones found com- 

 monly in fishes, and called ' suborbitals' and ' superorbitals.' The lachrymal is the 

 most anterior of the suborbital series, and is the largest in fishes ; it is also the most 

 constant in the vertebrate series, and is grooved or perforated by a mucous duct. 

 These ossicles appertain to the dermal or muco-dermal system or ' exoskeleton ;' not to 

 the vertebral system or ' endoskeleton.' 



The little slender bone, marked Hi' in fig. 13, has one of its extremities in the form 

 of a long, narrow, elliptic plate, which is applied to the ' fenestra ovalis' of the internal 



