72 Proceedings of the Royal Irish Academy. 



meat agrees more closely with that found in Arctopithecus than it does 

 with the condition in our specimen. 



Pronator quadratus has a broader attachment to the ulna than to 

 the radius, the reverse apparently obtaining in Professor Humphry's 

 specimen, though it is not quite clear whether his description refers to 

 TJnau or to Ai. 



Plexor carpi radialis extends in both specimens from the inner 

 condyle of the humerus to the scaphoid and flexor digitorum profun- 

 dus and sublimis, and palmaris longus presented the same features in 

 the two. The two latter muscles are fused for the upper part of their 

 course, but near the distal end the former of the two becomes separate 

 as a small muscle ending in two tendons to the two digits; the main 

 part of the muscle ends also in two tendons to the digits. The first 

 named of the three is quite distinct, arising from the outer condyle of 

 the humerus, from the forearm bones, and from the tendons of the radial 

 and ulnar flexors of the wrist, as well as from the tendon of palmaris ; 

 it also sends two tendons to the terminal phalanges of the digits. 



Plexor pollicis longus was not represented in our specimen, and 

 Professor Humphry makes no mention of it. 



Plexor carpi ulnaris is a curious muscle, consisting of two parts ; 

 the upper one of these arises from the back of the internal condyle and 

 from the hinder border of palmaris (?), becomes tendinous at the mid- 

 dle of the forearm, and is inserted into the outer border of the radius 

 posterior to and confluent with the insertion of supinator longus, and 

 covering over the attachment of extensor carpi radialis ; it is also in- 

 serted into the fascia of the back of the forearm ; the deep part, which 

 appears to be the normal ulnar flexor, arises from the olecranon, from 

 the lower border of anconeus, and from the whole inner edge of the 

 ulna, and is inserted into the pisiform bone. Professor Humphry also 

 describes it as consisting of two parts, but the upper one, whilst in the 

 main agreeing as to its origin with the foregoing description, becomes 

 fused with supinator longus, and is inserted into the palmar fascia, pisi- 

 form, and margin of the ulna.* The deep part had the same arrange- 

 ment as in our specimen. The separation into two parts of this muscle 

 in Choloepus is foreshadowed in the Three-toed Sloth, where the origin 

 is bicipital and the two parts remain separate for a long distance, but 

 there is no tendency to union between it and supinator longus. 



Supinator brevis is large, inserted into the uj^per one- third of the 

 radius, and pierced by the posterior interosseous nerve, which forms 

 much the larger part of the radial nerve. 



Extensor carpi radialis is single, arising from the outer humeral 

 condyle and from the radius, and ending in two tendons, one being at- 

 tached to the upper two-thirds of the second metacarpal bone, and the 

 other to the proximal end of the third metacarpal, Professor Humphry 



* It is possible that this may be a clerical error, as the ulnar attachment of sup. 

 long, is not mentioned by Professor Humphry. 



