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Show 1896.] MYOLOGY OF RODENTS. 169 ligament was seen in Rhizomys running from the axillary border of the scapula, between the origins of the teres major and minor, across the latter muscle to the metacromion process. A similar ligament has already been described in Lagostomus \ Biceps Cubiti.-There can be no doubt that, speaking generally, one of the characteristics of the Myomorpha is a double-headed biceps. This was noticed in every specimen which I dissected. Milne-Edwards, however, found only one head in Siphneus, but it is possible that further investigation may prove that this was merely an individual variation. In Hydromys Windle does nob notice the condition of the biceps. As a rule the insertion is into both bones of the forearm, but in Cricetus and Myoxus the muscle only goes to the radius, while in Rhizomys the ulna is the only bone to which it is attached. In Georychus and Bathyergus the two heads are easily separable down to the insertion by a little force. In the former the coracoid head goes entirely to the radius, the glenoid head to the radius and ulna; in the latter both heads can be traced to both bones. Coraco-brachialis.-In the Myomorpha the most usual arrangement is to find the second and third parts, described by Wood2, present; they are, however, fused, and the muscle has one continuous insertion from the middle of the humerus to the internal condyle. This description applies to Rhizomgs, Siphneus, Microtus, Myodes, Heteromys, Hydromys, and the Murinae. The Cricetinae (Cricetus and Cricetomys) have the same arrangement, but in addition the first part or rotator humeri is present. In Gerbillus and Myoxus only the second part was seen. In Georychus the muscle was absent, while in Bathyergus it was very small, and w7as only represented by the second part. Milne-Edwards says that the muscle is absent in " le Eat-Taupe du Cap," by which, 1 suppose, Bathyergus is meant. In all the animals dissected, as in other Rodents, the musculo-cutaneous nerve passes above the second part of the muscle. Brachialis Anticus.-All the Myomorpha have the external and internal heads of the brachialis anticus, and these are more or less completely fused; perhaps Bathyergus shows them most clearly separated from one another. The insertion, in every case that I dissected, was into the ulna only, but Milne-Edwards describes an additional feeble attachment into the head of the radius in Siphneus. Triceps and Anconeus.-There is no difference between the Myoraorphine triceps and that of other Rodents. In Cricetomys it was noticed that the outer head was inserted largely into the fascia of the outer side of the forearm. Bathyergus resembles Castor in the great development of the muscle, and in the fact that it is attached to both sides of the olecranon, as well as to the top. The anconeus has the usual attachments, and shows nothing of special interest. 1 P. Z. S. 1894, p. 2(33. 3 Journ. of Anat. vol. i. p. 45. |