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Show 1894.] MYOLOGY OP RODENTS. 271 In Ccelogenys the muscle is interrupted by three palmar cartilages Fig. 5. PAIM. B R W PlS.1 £LEX .CARP UlN. PALM - LONG-ABDUCTOR POL- . -FLEXOR T6 N P O M 3 , Right fore foot of Ccelogenys paca. Flexor Brevis Manus.-This muscle rises from the palmar ossicle on the radial side of the palm, and runs obliquely across to form the flexor perforatus for the fifth digit, usually joining the small flexor sublimis slip to that digit. It is supplied by the ulnar nerve. Muscles of the Thumb.-Owing to the slight development of the thumb these muscles are difficult to define accurately. The abductor pollicis is the most definite; it always rises from the radial part of the palmar cartilage, and is inserted into the base of the proximal phalanx of the thumb. In the Dipodidae and Caviidae this and the other thumb-muscles are practically absent. W h e n the flexor brevis is present it rises either from the semilunar cartilage over the bases of the metacarpals (as in Ccelogenys) or from the palmar cartilage (Capromys according to Dobson l). The opponens consists of a very few fibres ; it is found in most of the Sciuromorpha except Castor; its attachments are from the above-mentioned semilunar cartilage to the metacarpal bone. The adductor is best marked in the Octodontidae (Octodon, Myopotamus, and Capromys x) ; in Myopotamus it is quite distinct, 1 P. Z. S. 1884, p. 234. |