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Show 172 DR. R. W. SHUFELDT ON [Apr. 1, of this muscle, and the next one to be described, in Heloderma, I would say that I have found fundamental differences in both of them as compared with the corresponding muscles iu other Lizards, as they are described for us by the various authors before me, for a number of forms. So different, indeed, did I find the present one, that I dissected it out in three forearms of three separate individuals ; not only that, but I was not satisfied until I had again gone over all the other muscles of the forearm, removing them one at a time until only the flexor perforans digitorum and the flexor perforatus digitorum remained. The present muscle was found to be the same in all of these specimens. It arises by a broad and common tendon, in two well-defined parts, from the internal condyle of the humerus. Of these the larger and more massive part arises on a line below the origin of the flexor carpi radialis, while the origin of the second part is to be sought beneath the tendon of origin of this last-named muscle. Nice discrimination is required to properly separate these muscles at their common origin ; and Sanders found that in Liolepis the flexor carpi radialis and the flexor perforans digitorum were inseparable in this part of their course. Returning to the first part of the muscle we have now under consideration, we find that it stretches between the internal humeral condyle and the pisiform bone of the carpus, its carneous portion forming a muscular mass, of no inconsiderable bulk, at the middle of the flexor aspect of the forearm. Its insertion covers the entire palmar surface of the pisiform bone, the insertion of the tendon of the /. carpi ulnaris being found to its outer side. At the middle of the forearm, over the interosseous space, this part throws off a flat, muscular slip, which, becoming tendinous just before arriving at the wrist, joins the tendons of distribution of the second part of the flexor perforans digitorum, and with them passes beneath the annular ligament of the carpus. Now both of these parts of our present muscle not only have an origin from the internal condyle of the humerus, as I have already described above, but they both likewise arise from the entire length of the contiguous surface of the shaft of the ulna : this division of the origin is quite free from the belly of the smaller, or second part of the/, perforans digitorum, but it becomes far more intimate with it at the carpus, at the point where the tendon commences that passes beneath the annular ligament to go to the fingers. This last-mentioned tendon still remains to be described. A large, flat sesamoid occurs in the broad and compressed trunk of this as it passes over the wrist-joint. In the palm the tendon splits into five strong slips, and these are distributed in regular order to the five digits, each one passing to the end of its proper finger to be inserted into the base of the ungual phalanx, upon its flexor side. A triangular muscular slip of some considerable size is given off from this tendon as it passes over the wrist, and its fibres converging they become inserted into one or two of the mid-carpal bones. Sanders found a muscular development similar to this in Liolepis. The muscular slip that goes to the pollex digit apparently does not give off either |