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Show 1894.] ANATOMY OF ORNITHORHYNCHUS. 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 externus.-Is a small muscle having the usual origin and insertion. It is supplied by a branch of one of the nerves which supplies triceps. Anconeus internus.-Passes from internal condyle to olecranon. It is supplied by the ulnar nerve. MUSCLES OF THE FOREARM. Flexor digitorum.-This is a large muscle. It arises by three heads:-(a) from the internal surface of the ulna; (/3) 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 Mivartl in Iguana. TAVO 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 sublimis. 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 1 " Myology of Iguana," Mivart, P. Z. S. 1867, p. 785. |
