1894.] AKATOirr OF ORIflTHORHTUCHTJS. 699 



heads. The long head may be split up into three portions. It 

 arises from the glenoid ridge, on outer surface of scapula, and 

 passes down as a large separate muscle to the large expanded 

 olecranon. The inner head, also large, arises from and covers 

 the posterior surfaces of humerus ; it is inserted into olecranon 

 beneath outer and long heads. The outer head, smaller and 

 longer, arises by a narrow tendon from outer surface ; it blends 

 with the long head at olecranon. Beneath the inner head is a 

 fourth head, arising from posterior surface of humerus just above 

 the lower extremity ; it is inserted into the olecranon beneath 

 inner head. It is this portion of the muscle with which the 

 anconeus externus is continuous. Coues describes this part of 

 the muscle as a portion of anconeus. 



The triceps is supplied from posterior trunk of brachial plexus. 



Anconeus eMernus. — Is a small muscle having the usual origin 

 and insertion. It is supplied by a branch of one of the nerves 

 which supphes tricep?. 



Anconeus ^niernus. — Passes from internal condyle to olecranon. 

 It is supplied by the ulnar nerve. 



Muscles of the Foeeaem. 



Flexor digitorum. — This is a large muscle. It arises by three 

 heads : — (a) from the internal surface of the ulna ; (j3) from the 

 lower end of humerus; (y) a central portion also arises from 

 lower end of humerus. The three portions blend in the lower 

 part of the forearm, where the muscle becomes tendinous, just 

 above the wrist. The tendon expands into two portions, inner 

 and outer, each portion containing a sesamoid bone. From the 

 outer of these divisions tendons pass to the terminal phalanges of 

 the fourth and fifth digits ; from the inner, tendons pass to the 

 first, second, and third. At the under surface of the muscle at 

 the wrist is a strong tendinous band arising from cuneiform and 

 passing to the sesamoid bone in the radial division of the tendon. 

 The whole muscle has a very regular arrangement. The ulnar 

 portion is supplied by the ulnar nerve, i. e., the larger posterior 

 portion of the plexus, from seventh and eighth C. and first D. ; the 

 central and humeral portions are supplied by median nerve. Four 

 heads to this muscle are described by Mivart ^ in Iguana. Two 

 are humeral, one is ulnar. His fourth head arises from the carpus 

 and is inserted into the deep surface of a tendon containing a 

 palmar sesamoid. The tendinous band mentioned above might 

 represent the fourth head of the muscle as described by Mivart in 

 the muscle of this Saurian. 



Flexor sublimis digitorum. — There is a small subhmis. It 

 consists of four distinct muscular bellies. They arise from the 

 front part of the tendon of longus (profundus), which contains the 

 sesamoid bones. They pass to the first, second, third, and fourth 

 digits. The fibres of these small muscles arise both from the 

 * " Myology of Iguana," Mivart, P. Z. S. 1867, p. 785. 



