178 ANATOMY OF VERTEBRATES. 



fig. 108, the bone c, fig. 107, might be taken for a connate 

 f scapholunar.' In both tortoise, terrapene, and turtle, the distal 

 row of carpals consists, as in the Toad, of five bones, one to each 

 of the five metacarpals. About their homology there is no diffi- 

 culty: the bone, fig. 107, i, which supports the pollex, l, is the 

 trapezium ; the next 2, the trapezoides ; the third 3, the magnum ; 

 and the fourth and fifth are the two parts showing the type-state 

 of the connate bones, called ' unciform ' in mammals. A bone 

 analogous to a 'pisiform, f, fig. 107, is attached to the ulnar 

 division, 5, of the unciform, and, usually, also articulates with the 

 cuneiform in the Turtle. In Chelys and Trionyx, the bone 

 ansAvering to a, e, fig. 108, is divided ; the part, e, answering to 

 the ' intermedium ; ' Trionyx has also a ' pisiform.' The carpus 

 in most Lacertians, e.g. in Varanns niloticus 1 , has the scaphoid 

 reduced, as in Chelone, to the intermedial portion ; but the trape- 

 zium unites directly with the lunare, and this articulates exclu- 

 sively with the radius, simulating the scaphoid in position ; it 

 has, however, on its ulnar side, the ' cuneiform ' articulating with 

 the ulna, and a ' pisiform ' terminates the proximal row. The 

 distal row consists of five distinct bones ; the unciform beins 

 divided, as in Chelonians. In the Chameleon, fig. 110, the 

 proximal carpal series consists of the bones c and d, answering to 

 the two respectively articulating with the radius and ulna in 

 Varanus, and with those marked c and d in fio-s. 107 and 108. 

 The second carpal row has received two interpretations. In one 

 they are represented by the five subelongate bones having the 

 distal joints of metacarpals ; in the other they have coalesced into 

 the single bone c, which otherwise would be merely an enlarged 

 ' intermedium.' We shall afterwards see how the principle of 

 s serial homology ' helps in the solution of such problems. The 

 five bones radiating from the bone c are metacarpals ; the first 

 supports two, the second three, the third four phalanges, as in other 

 Lacertians ; and the equality of length in the opposing pair of 

 digits, IV and v, is preserved by the deduction of a phalanx from 

 the lacertian number. 



The correspondence of the Chameleon's scapular arch with that 

 of the Crocodile has been adverted to ; and, similarly, the distal 

 row of carpals is reduced to a single bone, fig. 109, f, in the 

 Crocodile, supporting the medius, in, annularis, iv, and minimus, 

 v, digits ; and answering to the magnum and unciforme connate. 

 The proximal row includes three bones answering to the lunare, 

 c, and cuneiforme, d, in Chelone, fig. 107, and Chameleo, fig. 110; 



1 CLi. pi xvu, tig. 45. 



