44 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XIV. 



runs direct to the common palmar tendon which it joins next to that of 

 the ulnar head and entad of that of the second head. 



4. The fourth head, which is almost as large as the first or ulnar 

 head, has origin from a distinct slip from the front of the inner condyle 

 of the humerus and from a broad fleshy expansion arising from the inner 

 side of the proximal fourth of the radius. The two fleshy parts join to 

 form a single tendon which runs along the radius to join the common 

 tendon in the palm. 



While obviously very different from that of Didelphis, in which there 

 is no division above the palm, this muscle is so variable that detailed 

 comparisons have not been attempted. In most marsupials it sends 

 tendons only to the four ulnar digits. 



Abductor pollicis longus (Extensor ossis metacarpi pollicis). Lies 

 in the deep groove in the proximal part of the ulna and takes origin from 

 the adjacent sides of the ulna and the radius, the fibers converging from 

 the two sides to the central tendon which extends some distance into 

 the fleshy part. Its origin (male specimen) is thus some 5 mm. in 

 length. Its rather broad flat tendon passes beneath the ulnar and lateral 

 digital extensors crossing the forearm and becoming superficial between 

 the extensor digitorum communis and the extensor carpi brevis. It then 

 curves around the radius and inserts on the lateral surface of the first 

 metacarpal. 



Pronator quadratus. This muscle, which is present in didelphids 

 and so far as known in all other marsupials except Notary ctes, is not found 

 in Ccenolestes, or at most is represented by no more than an indefinite 

 non-muscular fascia. It is reported as poorly developed in Thylacinus, 

 Sarcophilus, Phalanger and Phascologale. It is lacking in monotremes, 

 insectivores, bats, and certain edentates (Dasypodidae, Manidae). 



Brachioradialis (Supinator longus) . Origin from the outer epicondy- 

 lar ridge of the humerus proximad of the extensor carpi radialis longus. 

 Its tendon passes under that of the abductor pollicis longus and over a 

 groove in the extremity of the radius to insertion in the external lateral 

 ligament which overlies the extremity of the radius. 



Extensor carpi radialis longus. Origin from the outer epicondylar 

 ridge of the humerus distad of the brachioradialis. Insertion on the base 

 of the second phalanx of the second digit. 



Extensor carpi radialis brevis. Origin from the outer epicondylar 

 ridge and septa of the extensor digitorum communis, between which and 

 the extensor carpi radialis longus it lies. Insertion on the outer lateral 

 surface of the proximal third of the first phalanx of the third digit. It 

 is somewhat larger than the longus and separate from it as in Thylacinus 

 and Phalanger. In most other marsupials, the long and short radial 



