190 DR. R. W. SHUFELDT ON [Apr. 1, 



(4) Arising from the next inner ossicle of the distal tarsalia, but 

 not passing through the tendinous slips of the extensor longus 

 diyitorum, this has an insertion similar to the last, but here upon 

 the second digit. 



(5) The fourth digit is similarly supplied, only in its case the 

 fasciculus arises from the extreme end of the fibula, and it has 

 likewise two lateral slips, one upon either side, inserted upon the 

 dorsal aspect of its proximal phalanx, and these arise on either side 

 from the bases of the proximal joints of the third and fifth digits. 

 So it will be seen that not only in this, but in other particulars, the 

 ))resent muscle differs from the corresponding one in Iguana, as 

 described for us by Mivart (P. Z. S. 1867, p. 794). 



107. Popliteus. — Heloderma has this muscle comparatively very 

 large. It arises from the tibial side of the fibula, for about its 

 proximal fourth, and passing obliquely downwards and inwards is 

 inserted into the shaft of the tibia for nearly the entire length of its 

 fibular aspect. At the back of the leg, at its origin and for some way 

 bevond, it is somewhat intimately attached to ilm flexor longus digit- 

 orum that covers it ; while in passing to its insertion it fills in much 

 of the interosseous space with its flat, triangular muscular expanse. 



108. Peroneo-tiLiul. — Anteriorly, and belonging to the deep set, 

 we have this interesting muscle. It spans the inter-tiljio-fibular 

 space below. Arising from the lower third of the shaft of the tibia, 

 its fibres pass across to become inserted into the corresponding 

 extremity of the shaft of the fibula. Behind, it is largely covered 

 by the tibialis posticus, as the latter passes to its insertion. 



109. Tibialis posticus. — As is commonly the case among Lizards, 

 this muscle possesses a triangular form with its apex above. It 

 arises from the inner aspect of the fibular shaft, tibiad, for the 

 distal half of its extent. Its fibres converge as they pass downwards 

 and inwards, and when near the tarsus they become strongly ten- 

 dinous, which tendon is powerfully inserted into the tibial ossicle 

 of the co-ossified elements of the proximal row of the ankle. Over 

 the lower part of the tibia, a firm fascia fuses with the tendon of 

 this muscle, which there spreads out to cover to some extent the 

 tarsal joint, to which it gives a certain strength and support. 



110. Flexor longus digitorum {perforans). — Large and carneous 

 in its upper part, this muscle arises from the posterior aspect of the 

 external condyle of the femur ; from the posterior aspect of the 

 proximal half of the shaft of the fibula; and from the tendon of the 

 external head of the gastrocnemius muscle. It is also quite 

 intimately attached to the underlying popliteus at its origin. From 

 these several points the Jiexor longus digitorum, as a muscle of 

 some considerable bulk, passes down the back of the leg to 

 become, near the ankle, quite suddenly flat and then completely 

 tendinous. It passes dorsad of the tendinous arch at the ankle, 

 and in the sole of the foot sphts into five small tendons, which 

 are distributed, one to each, to the five pedal digits. Each 

 perforates the tendons of the Jiexor brevis digitorum, after which 

 they send to the joints of the toes as they go to their distal iuser- 



