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Show 262 MR. F. G. PARSONS ON T H E [Mar. 20, comes from the spine of the scapula and fascia over the infraspinatus. Mivart and Murie, in their description of the myology of the Agouti \ prefer to describe the clavicular portion as part of the pectoralis, but I have been able to satisfy myself that its nerve-supply is derived from the circumflex and not the anterior thoracic. The insertion of the deltoid is into the pectoral ridge close to that of the pectoralis. The clavicular fibres are often prolonged to the elbow and in all cases are inserted lowest, while the part from the spine is inserted deep to the acromial slip. In the Dasyproctidae the clavicular portion is continued down almost to the external condyle. In Sciurus and Pteromys the clavicular and acromial fibres are closely united owing to the development of the clavicle. Sphingurus has the same arrangement. In Arctomys and Spermophilus the clavicular part divides into a superficial and deep portion; the latter has the usual insertion, but the former is continued down to the coronoid process of tbe ulna. In Castor, owing to the great development of the muscle, the intervals between the three parts are slight. The other animals examined present nothing remarkable in this muscle. Supraspinatus, Infraspinatus, and Subscapular is.-These muscles have the human attachments and, except in their comparative size, do not vary at all. Teres Major.-This muscle rises from the posterior quarter (more or less) of the axillary border of the scapula, and is inserted either into the tendon of tbe latissimus dorsi or into tbe humerus close to the insertion of that muscle. In the Dipodidae the insertion is posterior to that of the latissimus dorsi as in M a n (D. cegyptius, D. hirtipes, Alectaga inclica). In the Octodontidae it is inserted into the front of the tendon of latissimus dorsi (Aulacodus, Myopotamus, Octodon, Capromys pilorides and C. melanurus)2. In Lagostomus among the Chinchillidae, owing to the great size of the infraspinatus, the muscle only rises from about gth of the axillary border of the scapula and from the surface of the infraspinatus and subscapularis, which overlap the bone. The insertion is into the rudimentary bicipital groove somewhat above the latissimus dorsi tendon, with which it is closely connected. Chinchilla has very much the same arrangement, but the muscle rises from more of the axillary border. In the Hystricidae the lower border of the muscle is wrapped round by the latissimus dorsi close to the insertion (vide latissimus dorsi) (Hystrix, Sphingurus). In the Dasyproctidae it was inserted nearer the shoulder than the latissimus dorsi in m y specimen of Dasyprocta, but according to Mivart and Murie 3 the two muscles are inserted together. In Ccelogenys it is inserted with, and in front of, the latissimus dorsi. 1 P. Z. S. 1866, p. 383. 2 Dobson, P. Z. S. 1884, p. 234. 3 P. Z. S. 1866, p. 383. |
