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Show 176 DR. R. W. SHUFELDT ON [Apr. 1, reptile. There were found to be five of them, and they passed from the tendon-slips of the /. perforans digitorum in the palm 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 Mivart has carefully described these as they occur in Iguana tuberculata (P. Z. S. 1867, p. 785). 54. Interossei palmares.-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 writh 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 comes 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 tuberculata 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 metacarpal 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 metacarpal 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 interossei dorsales. |