1894.] 



MYOLOGY OF RODENTS. 



271 



In Coelocjenys the muscle is interrupted by three palmar 

 cartilages. 



Kg. 5. 



ABOUCTOR 

 " POi. . 



FUEX .CARP 

 U lK. 



PALM. LONG... 



FLEXOR 

 TS NdoMS . 



Eight fore foot o^ Ccelogenys paca. 



Flexor Brevis Manns. — 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 poUicis 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 Caviidse 

 this and the other thumb-muscles are practically absent. 



When the flexor brevis is present it rises either from the semi- 

 lunar cartilage over the bases of the metacarpals (as in Ccelogenys) or 

 from the palmar cartilage (C'apromys according to Dobson ^). 



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 OctodontidsB (Octoclon, 

 Myopotamus, and Capromys ^) ; in Myopotc(mus it is quite distinct, 



» P. Z. S. 1884, p. 234. 



