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Show 1896.] MYOLOGY OF RODENTS. 171 In Microtus, Rhizomys, Bathyergus, and Hydromys, however, only three lumbricals 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 Myoxus and Microtus it occupies the middle third of the forearm; in Cricetomys, Cricetus, and Mus barbarus 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 Georychus, Bathyergus, Rhizomys, 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 Hydromys, 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 Radialis Longior and Brevior.-In all the animals examined these muscles had the usual attachments. W h e n there is any difference in size, as in the case of Myoxus, Georychus, Rhizomys, and Siphneus, the brevior is the larger muscle. Milne-Edwards says that in Georychus and Spalax 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 he very close to one another. Extensor Communis Digitorum.-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 barbarus no slip is given to the little finger. In Cricetomys two tendons pass to the middle, and in Rhizomys two to the ring finger. Extensor Minimi Bigiti.-The insertion of this muscle was into the fourth and fifth fingers in Gerbillus, Microtus, Myodes, Mus barbarus, Hydromys, 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 Ulnaris.-Nothing special was noticed in the attachments of this muscle. Milne-Edwards describes it as 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 what he |