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Show 1894.] MYOLOGY OP RODENTS. 263 In the Caviidae the arrangement is the same as in Ccelogenys (C. cobaya, Ceredon rupestris). Teres Minor.-The teres minor rises from the humeral third to half of the axillary border of the scapula, and is inserted just below the insertion of the infraspinatus. It is sometimes a perfectly distinct muscle, but in most cases is so closely united to the infraspinatus that, were it not for its being supplied by tbe circumflex nerve, it would be most conveniently described with that muscle. The teres minor was seen most distinctly in Lagostomus, in which animal a fibrous band was found running from the metacromial process to the origin of the long head of the triceps, covering the infraspinatus and teres minor near their insertions. In the Sciuromorpha the muscle is specially indistinct. Biceps Cubiti.-The biceps always rises by a strong tendon from tbe margin of the glenoid cavity at the base of the coracoid process ; it may or may not have a second head rising from the tip of that process, or from the surface of the coraco-brachialis. Its insertion is into the radius, ulna, or both bones just below the sigmoid cavity, occasionally, however, it is prolonged farther down the bones. The semilunar fascia from the inner side of its tendon to the fascia of the forearm is very indistinct, but by careful dissection a few fibres may be traced. In the Dipodidae there is only one head, and the insertion is almost entirely into the ulna (Dipus cegyptius, Alectaga indica). In the Octodontidae there are two heads; the insertion is into both radius and ulna (Myopotamus, Aulacodus, Capromys, Octodon). In the Hystricidae there is only one head in Hystrix, but two in Sphingurus and Erethizon dorsaius 1; it is inserted largely into the radius in the Tree-Porcupines, but chiefly into the ulna in Hystrix. In the Chinchillidae there are two heads; the insertion is into the coronoid process of the ulna and the oblique line of the radius (Chinchilla, Lagostomus). In the Viscacha I dissected there were three heads to the biceps on the left side, the extra one rising from the front of the great tuberosity of the humerus. In the Dasyproctidae there is only one head, and the insertion is entirely into the ulna (Dasyprocta, Ccelogenys). In the Caviidae the arrangement is tbe same as that in the Dasyproctidae (Cavia cobaya, Ceredon rupestris, Dolichotis2). In the Sciuromorpha, Sciurus, Pteromys, Arctomys, and Xerus have the muscle rising chiefly by tbe glenoid or long head, but also by some fibres from the front of the coraco-brachialis (representing a short head). The insertion is almost entirely into the tubercle of the radius so as to act as a supinator. Spermophilus differs in the absence of tbe short head. Castor has only one head and the insertion is entirely into the ulna. Coraco-brachialis.-The three parts of this muscle described by 1 Mivart, P. Z. S. 1882, p. 271. 2 Beddard, P. Z. S. 1891, p. 236. 18* |
