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 in 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 

 on\y the flexor perforans diyitoriim and the flexor per/or atus 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 digitoruia were 

 inseparable in this part of their course. 



Returning to the first part of the muscle we have now under con- 

 sideration, 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 f. carpi uhiaris 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 

 o'l the f. 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 

 [26] 



