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Show 1890.] HELODERMA SUSPECTUM. 173 auxiliary muscular slips or tendons, but simply passes through the semitendinous tube developed for it by the flexor perforatus digitorum. At the point of bifurcation, from the dorsal aspect of the tendon-slip that goes to the second digit, w e find two muscular slips given off: the one on the ulnar side distally forms a slender tendon which joins the corresponding tendon of the flexor perforatus digitorum; the one on the radial side inserts itself into the base of the proximal joint of the corresponding phalanx. This arrangement also obtains in the case of the third and fourth digits, and to a considerable extent with the fifth digit also. 48. The Flexor perforatus digitorum, as in so many lizards, is a muscle confined to the palm of the hand. In the reptile before us it arises by a c o m m o n tendon from the pisiform bone and to some extent from the annular ligament of the wrist. From its point of origin it immediately radiates in the direction of the fingers, primarily dividing into five slips, each one going to its proper digit, and together forming a comparatively thick muscular pad for the palm of the hand. Each and all of these slips are quite distinct, and the one devoted to the pollex is especially thick : this latter at its insertion develops two small tendon-slips which attach, upon either side, to the proximal end of the first phalangeal joint at its latero-palmar aspect, and between these passes the tendon of the deep flexor which goes to this digit. A firm connective tissue both extensively and intimately surrounds the joint at this point, and has to be dissected away before the true relations of the parts can be clearly seen ; and, further, we find that a tubular canal arises in this locality, stretchiug longitudinally along the nether aspect of the phalanx, being attached to its sides, and through it passes the digit-tendon of this finger furnished by the deep flexor. In the case of the second finger the arrangement is essentially quite different from what I have just described it for the thumb; and here, too, as already pointed out above, the power of the muscle is augmented by the reception, at its ulnar side, of an auxiliary slip offered on the part of the deep flexor. W e also find the fibrous, tubular canal present, as already described, and in this finger, as is indeed the case with all of the remaining phalanges, this tube abruptly terminates at the middle of the joint next behind the ungual one, at its palmar aspect, while an inner secondary tube also presents a terminal aperture opposite the middle of the proximal phalanx. Returning, now, to the difference in the arrangement of the tendons in this finger, I would point out the following interesting structures : instead of the insertional tendon-slip of the flexor perforatus digitorum of the second digit becoming inserted on either side of the proximal joint at its base, as is the case in the pollex, and thus allowing the deep tendon of the perforans to pass between them, it splits, and allows the same to pass through the perforation, but after that this slip-tendon of the perforatus is inserted as a single cord into the base of the second phalanx of the digit. Here I will also invite attention to some other structures, which perhaps more properly should have fallen under m y description of PROC. ZOOL. Soc-1890, No. XIII. 13 |