76 Proceedings, oj the Royal Irish Academy. 



quioquesection of the leg, the latter tendon going to be inserted into 

 the OS calcis external to the former, and qaite separate from it; the 

 origin of internas is from the lower back portion of the femur and is 

 devoid of a fabella. A similar arrangement is described by Professor 

 Humphry, with the exception of the two tendons of insertion of 

 externus. 



Plantaris is not represented in either, though Professor Humphrj", 

 judging by the arrangement in Gyclothurus, seems to think that it is 

 involved in gastrocnemius externus, and regards the popliteal slip of 

 soleus as correspoding to the external portion of the gastrocnemius in 

 Gyclothurus. It was largely developed in Arctopithecus. 



Flexor digitorum longus and Plexor hallucis longus are fused, but 

 divide into three tendons before reaching the ankle joint ; one tendon 

 goes to each digit and receives the tendon of the combined tibialis 

 anticus and extensor longus. Professor Humphry in his description of 

 flexor digitorum says that it arises from the tibia, fibula, and slightly 

 from the popliteal sesamoid, the tibial portion being deep and covered 

 by the fibular part, as w^ell as by tibialis posticus ; the foi'mer of these 

 represents the flexor of the fingers and the latter that of the thumb. 

 The arrangement is more complex in Arctopithecus, where we find flexor 

 digitorum existing as a tricipital muscle taking origin from the upper 

 and back part of the tibia, from the middle of that bone, and from the 

 greater part of the fibula and external lateral ligament of the knee, and 

 receiving the tendon of plantaris ; flexor hallucis arises from the fibula 

 and interosseous membrane, and unites "with it, the two subsequently 

 dividing into three tendons. The first of these origins of flexor digitorum 

 is alone described by Professor Macalister in Bradypus, and Dr. 

 Humphry found in that animal that it consisted of three parts repre- 

 senting respectively plantaris, flexor digitorum, and flexor hallucis. 



Plexor digitorum brevis arises from the calcaneum, and is inserted 

 into the sheath of the flexor tendon of the middle digit. Professor 

 Humphry found a totally diff'erent arrangement, for this muscle in 

 his specimen was in three parts, one bicipital from entoeuneiform and 

 OS calcis, the other two from os calcis ; they all terminate in the 

 sheaths of the flexor tendons. 



Plexori longo accessorius is very large, arising from both sides of 

 the calcaneum and inserted chiefly into the tendon of the outer toe ; 

 it was continuous "with soleus in Professor Humphry's specimen. 



Tibialis posticus is arranged quite difi"erently in the two specimens. 

 In ours it was perfectly normal, extending from the tibia to the 

 entoeuneiform ; in Dr. Humphry's it consisted of two parts, the ten- 

 don of the larger of which runs behind the inner malleolus, sends a few 

 fibres to the entoeuneiform, but is mainly attached to the second meta- 

 carpal ; the tendon of the smaller internal portion runs in a separate 

 channel in the malleolus, and passing over the inner cuneiform, becomes 

 continuous with a portion of the short flexor of the fingers, whose ten- 

 don blends with that of flexor brevis to the fourth digit. The arrange- 

 ment in A'i agrees in the main with that in our specimen. Tibialis 



