1890.] HELODERMA STJSPECTUM. 173 



auxiliary muscular slips or teudoiis, but simply passes through the 

 semitendinous tube developed for it hj the flexor perforatus diyitorum. 

 At the point of bifurcation, from tiie dorsal aspect of the tendou-slip 

 that goes to the second digit, we 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 digito7'um, as in so many lizards, is a 

 muscle confined to the palm of the hand. In the reptile before us it 

 arises by a common 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 formiog 

 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 fiexor 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, stretching longi- 

 tudinally along the nether aspect of the phalanx, being attached to 

 its sides, and through it passes the digit-tendon of this finger fur- 

 nished 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. We 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 jiroximal joint at its base, as is the case 

 in the pollex, and thus allowing the deep tendon of tiie 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 



Here I will also invite attention to some other structures, which 

 perhaps more properly should have fallen under my description of 

 Proc. Zool. Soc— 1890, No. XIII. 13 



