Mackintosh — Muscular Anatomy of Oholoepus didactylus. 77 



anticus and extensor hallucis occupy a very curious position; tlieir 

 origins, which are slightly separable from one another, extend down the 

 whole front of 'the tibia, and the lower two-thirds of the anterior bor- 

 der of the fibula, and becoming perfectly fused in front of the leg; the 

 tendon formed hy the two bellies winds round the ankle joint and is 

 inserted into the front of the flexor of the middle toe, thus converting 

 these two powerful muscles into flexors. Here again Dr. Humphry's 

 description, so far at least as the origin is concerned, differs -largely 

 from ours. He found the former of the two to consist of three parts, 

 one arising from the upper half of the tibia, one from the middle of the 

 fibula (extensor hallucis), and a third from the lower front part of the 

 fibula and from the malleolus ; this latter crosses the ankle to be in- 

 serted into the entocuneiform bone and base of first metatarsal, but 

 apparently quite separate from the rest of the muscle, whose two parts 

 unite into a tendon which subsequently divides into three going to the 

 flexor tendons of the three digits ; the two latter segments appear to 

 represent in their origins the entire fibular part in our specimen, but 

 Ave found no trace of the curioiis insertion of the third portion, nor yet 

 of the threefold attachment of the tendon from the first and second. 

 The tricipital origin also obtains in Arctopithecus and Bradypus, but 

 the insertion is into the entocuneiform and metatarsals. 



Extensor hallucis brevis is a small muscle extending from the 

 lowest one-tenth of the fibula to the rudimental hallux. 



Extensor digitorum brevis arises from the front of the tarsal 

 bones, and its three tendons are inserted into the deep surfaces of the 

 tendons of extensor longus. The origin in Professor Humphry's 

 specimen included the proximal parts of the metatarsals, as well as the 

 tarsals; the insertion was into the terminal phalanges of all the digits. 

 Transversalis pedis extended from the external metatarsal to the 

 base of the first phalanx of the inner toe, to which Dr. Humphry adds 

 a second insertion into the distal end of the first metatarsal. 



Extensor digitorum longus is a small muscle sending one tendon 

 to each of the three digits ; it supplied only the third and fourth digits 

 in Professor Humphry's specimen. 



Peronseus longus arises from the back of the fibula, and from the 

 popliteal sesamoid in our specimen, and is inserted into the base of the 

 fourth metatarsal, with slight attachments to the other three ; 

 peronseus quinti was absent, and we could find no trace of p. brevis, 

 though it is described by Professor Humphry as extending from the 

 malleolus to the base of the fifth metatarsal ; p. tertius is well deve- 

 loped in both, running from the front edge of the fibula to the fifth 

 metatarsal, with fibres to the fourth, as well as in Professor Humphry's 

 specimen. 



' Abductor interni digitiin our specimen stretches from the internal 

 plantar sesamoid to the sheath of the flexor tendon of the inner digit. 



The interossei are well developed, but present no modification of 

 any great importance, two being attached to each extensor, one on 

 each side . 



