1890.] MYOLOGY OF RODENTS. 171 



111 Microlus, Ithizomys, Bathyergus, and Ilydromys, however, only 

 three luinbricals were seen, the radial one having been suppressed. 

 Pronator Quadratus. — This muscle is less well developed as a 

 rule than in the Hystricomorpha, never, so far as I have seen, 

 extending along the length of the bones. In Myo.vtis and Microtus 

 it occupies the middle third of the forearm ; in Oricetomys, 

 Cricetus, and Mus harharus the lower half. In the Gerbille it 

 attains its maximum of development, and is attached to the lower 

 three-quarters of the two bones. In Georyclms, Bathyergus, 

 llhizomys, and Siphneus it is a very feeble muscle — in the two 

 former being found only opposite the insertion of the pronator 

 radii teres, while in the two latter it is represented by a few fibres 

 between the lower ends of the two bones. 



Supinator Longus. — This muscle was wanting in every animal 

 dissected. Windle found it absent in Uydromys, and Milne- 

 Edwards says that it is also wanting in Siphneus, Spalax, and 

 Helamys. He states, however, that it is present in the Hamster, 

 and, although it was most certainly absent in the Hamster I 

 dissected, I take his statement to mean that very occasionally a 

 supinator longus may be found among the Myomorpha as a 

 reversion to the Sciuromorphine type. 



Extensor Carpi Badialis Longior and Brevior. — In all the 

 animals examined these muscles had the usual attachments. 

 When there is any difference in size, as in the case of Alyoxus, 

 Georychns, Rhizomys,. and Siphneus, the brevior is the larger 

 muscle. Milne-Edwards says that in Georyclms and Sjjolax there 

 is only one radial extensor, but he does not mention where that 

 one is inserted. Unless the insertion is carefully looked for the 

 two muscles may easily be mistaken for one, as they lie very close 

 to one another. 



Extensor Communis JDigiiorum. — The only point of interest in 

 the Myomorphine common extensor is whether it goes to the 

 fifth digit or not. In Georychus, Bathyergus, Siphneus, and Mus 

 harharus no slip is given to the little linger. In Cricetomys two 

 tendons pass to the middle, and in Rhizomys two to the ring 

 finger. 



Extensor Minimi Digiti. — The insertion of this muscle was into 

 the fourth and fifth fingers in Gerhillus, Microtus, Myodes, Mus 

 harharus, Ilydromys, Georychus, Bathyergus, and Rhizomys. In 

 Bathyergus, however, the tendon to the fourth digit was very 

 small. In Cricetus it was attached to the third and fifth digits, 

 while in Myoxus and Cricetomys it only went to the fifth. 



Extensor Carpi Uhiaris. — Nothing special was noticed in the 

 attachmeuts of this muscle. Milne-Edwards describes it ns a 

 double muscle in Siphneus, one tendon going to the base of the 

 fourth, and the other to the base of the fifth metacarpal bone, 

 at the same time he does not describe any extensor minimi digiti. 

 Considering the very constant character of the extensor carpi 

 ulnaris in Rodents, and the comparative inconstancy of the 

 extensor minimi digiti, I expect that the explanation of vvhat he^ 



