OCR Text |
Show 1870.] MYOLOGY OF CHAM/ELEON PARSONII. Fig. 12. 867 4-_z? a Deepest muscles of extensor surface of right forearm. M. P. Extensor metacarpi poliicis. P. A. Pronator accessorius. P. Q. Pronator quadratus. S. L. Supinator longus. 1. The first part (fig. 13, T) arises from the axillary margin of the scapula, just behind (when the humerus is horizontal, above) the glenoid surface. This answers to both of the first two parts (external and internal long heads) of the triceps of the Iguaua; and a strong tendon on its inner surface indicates the part answering to the internal long head of that muscle in the last-named animal. 2. The second part arises from the whole posterior surface of the humerus and part of its outer and inner surfaces. Its origin extends upward (the humerus being placed vertically) to just below the head of the bone, and above the insertion of the second part of the deltoid. Inwardly it extends to just behind the insertion of the latissimus dorsi. Externally (fig. 13, T2) it reaches the posterior border of the brachialis anticus. 3. Tbe third part (fig. 8, T. I) is much the smallest, and is closely connected with the second part. It springs from the inside of the humerus, its origin rising to the level of the upper limit of the insertion of the latissimus dorsi. These three parts unite together, and are inserted in common into the proximal end of the ulna, a large sesamoid ossicle being situated, behind the elbow, in the tendon of insertion. The biceps (figs. 1, 8, 9, 10, 11, 13, 15, & 16, B) has a single origin, by a long and strong tendon, from the coracoid, just external to its sternal groove. This tendon is at first covered by fibres of the subclavius, and then passes over the short coraco-brachialis. Descending in front of the insertion of tbe pectoralis, it there becomes fleshy, and becomes more or less divisible into two bellies, which embrace the brachialis anticus in front, but leave part of the latter visible within and without the arm. It ends in two tendons, one for each belly (fig. 16, B), which, by their divergence, expose the brachialis anticus in the middle of the lower part of the upper arm. One of these tendons is inserted into the ulnar side of the front aspect of the radius, at the place of the tubercle; the other is inserted into the ulna, in front of its articular surface for tbe humerus. |