l/fi DR. R. W. SHUFELDT ON [Apr. 1, 



reptile. There weie found to be five of them, and they passed from 

 the tendon-sHps of the /. perfora7is diyitonim in the ])alm of the hand 

 to the corresponding tendons of the/, perforatus digitorum and the 

 bases of the proximal joints of the digits, as already pointed out 

 above. Professor jNIivart has carefully described these as they 

 occur in Iguana tubercidata (P. Z. S. 1867, p. 785). 



.54. Interossei pabnares. — There are three of these in the palm 

 of the hand of Heloderma ; they are unusually handsomely 

 developed, somewhat peculiar, and I have studied them with great 

 care, aided by a powerful lens. They arise by three thin, though 

 strong, tendons, from two bones of the second row of the carpus. 

 The first one springs from the outer one upon the ulnar side ; the 

 second one from the same bone as well as from the second in the 

 row ; the third conies off entirely from the second bone of the row. 

 The first-mentioned muscle enlarges and becomes carneous as it 

 passes forwards and is inserted, fleshy, into the distal extremity of 

 the shaft of the fourth metacarpal bone upon its palmar aspect and 

 just behind its head. Number two, or the middle one of the 

 three of these interossei palmares, possesses a similar form to the 

 one just described, and makes a similar insertion upon the shaft of 

 the third metacarpal. Finally, the one on the side of pollex is 

 inserted in a like manner into the second metacarpal. 



I am thus careful in presenting these insertions of the palmar 

 interosseous muscles, for the reason that Professor Mivart found 

 that in Iguana tubercidata they were inserted " one on each side of 

 the proximal phalanx of each of the three middle digits" (P. Z. S. 

 1867, p. 786). From their position here, it will at once be seen 

 that these muscles are not truly " interossei," but rather rest upon 

 the palmar aspects of the metacarpal bones, and it is from their 

 position in the hands of most mammals that the term has been 

 derived. 



55. Interossei dorsales. — The first of these arises from the radio- 

 palmar aspect of the base of the second metacarpal, and passing 

 obliquely forwards and outwards becomes inserted along the inner 

 side of the shaft of the pollex metacarpal, and distally by a tendon 

 into the base of the proximal phalanx of the same digit, at its 

 internal latero-dorsal aspect. We also note a thin, but rather 

 broad, tendon, stretching obliquely between the two metacarpals 

 here referred to, at their further extremities, the insertion upon the 

 second metacarpal being the higher on the shaft. The second 

 dorsal interosseous arises from the base of the third metacarpal at a 

 point corresponding to that, just described, on the second meta- 

 carpal as the origin of the first dorsal interosseous, and, passing 

 obliquely across, is similarly inserted into the proximal phalanx of 

 the second digit, and along the inner side of the shaft of its meta- 

 carpal bone. Similar interosseous muscles to these are found 

 between the digits and their metacarpal bones of the third and 

 fourth, and the fourth and fifth, phalanges, as are also the auxiliary 

 oblique tendons referred to above ; and thus it will be seen that 

 Heloderma possesses four hiterossei dorsales. 

 [30] 



