1894.] 



MYOLOGY OF RODENTS. 



269 



In Cavia cobaya there are two slips, the radial goes to the 

 index and middle, the ulnar to middle, ring, and little fingers. 



In Pteromys and Arctomys the radial slip goes to all the fingers, 

 while the ulnar only goes to the middle and ring. 



Fig. 4. 



Left fore foot of Castor canadensis (extensor tendons). 



Extensor Minimi Digiti. — The extensor minimi digiti rises from 

 the external condyle in common with the extensor communis 

 digitorum, and is usually inserted into the tendons of that muscle 

 on the dorsum of the 4th and 5th digits. Its tendons are also 

 usually connected to the ulnar sesamoid bones on the palmar 

 surface of the metacarpo-phalangeal joints. In the following 

 animals the insertion differed from the above description : — 



SpMngurug and Sciurus to 3rd, 4th, and 5th digits ; Chinchilla* 

 Pteromys, and Castor to 5th only. In Aulacodus the muscle 

 was completely fused with the extensor communis. From the 

 difference in the number of tendons in animals otherwise closely 

 allied I should suspect this muscle of being liable to a good deal 

 of individual variation. 



