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Show 1894.] MYOLOGY OF RODENTS. 261 In the Chinchillidae the muscles are largely attached to the clavicle. In the Dasyproctidae the scapulo-clavicularis is especially well developed, being considerably larger than the supraspinatus. In the Caviidae the small clavicle is between the two muscles in Cavia cobagct, having both attached to it ; but in Ceredon rupestris the subclavius was found to send a few fibres into the clavicle and a few into the scapulo-clavicularis, but its insertion was chiefly into the anterior border of the acromial process. Tbe scapulo-clavicularis rose chiefly from the clavicle. In the Sciuromorpha the subclavius had the usual human attachments, but the scapulo-clavicularis was absent in all the animals examined. It is interesting to notice that the Dipodidae, so far as this muscle is concerned, differ from all the rest of the Hystricomorpha. Tbe nerve-supply of both parts of this muscle is from a branch from the upper part of the outer cord of the plexus, corresponding to the human nerve to the subclavius. Fig. 2. Shoulder-muscles of Ceredon rupestris. 1. Deltoid (clavicular). 5. Trapezius (cut). 2. „ (acromial). 6. Subclavius. 3. „ (spinous). 7. Clavicle. 4. Levator clav. (cut). 8. Acromion and metacromion. Deltoid.-The deltoid in Bodents consists of three parts, which are liable to become more or less fused with one another. The first part rises from the outer part of the clavicle, the second from the acromial and metacromial processes, while the third part P R O C ZOOL. Soc-1894, JSTo. XVIII. 18 |