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Show 1896.] MYOLOGY OF RODENTS. 181 Extensor Longus Digitorum.--As in all other Rodents, this muscle rises by tendon from the front of the external condyle of the femur. In Mus barbarus, however, as in Sphingurus and Dipus, a few accessory fibres came from the head of the tibia. The insertion is into the second, third, fourth, and fifth toes except in Mus barbarus, where the slip to the little toe was wanting, and in Gerbillus, where there was in addition a feeble slip to the first toe. Extensor Proprius Hallucis.-This is always present and has the normal insertion. Its exact origin varies a good deal, and apparently is of little importance from a classificatory point of view. In Gerbillus, Myoxus, Mus barbarus, Georychus, and Bathyergus it rises from the second quarter of the fibula ; in Cricetomys, Cricetus, and Mus rattus from the third quarter; in Rhizomys, Microtus, and Heteromys from the middle two quarters. Extensor Brevis Digitorum.-As a rule this muscle has two tendons, one for the second, the other for the third toe ; this is the case in Cricetomys, Cricetus, Gerbillus, Rhizomys, Microtus, Heteromys, Mus barbarus and M. rattus. In Georychus the fourth toe has a slip as well. In Myoxus and BathyergusT was interested to find a distinct but small tendon to the proximal phalanx of the first toe, these being the only Rodents in which I have ever seen the extensor brevis going to the equivalent of our great toe. In no Rodent, so far as I know, is there ever a tendon to the fifth toe. Peroneus Longus.-This is always a constant muscle rising from the upper quarter of the fibula, and passing through a groove on the outer side of the external malleolus anterior to the other peroneal tendons. In no animal dissected does it call for any remark. Peroneus Brevis.-This arises from the middle two quarters of the fibula and passes between the tendons of the peroneus quarti and quinti digiti behind the external malleolus; it then runs above the peroneal spine on the calcaneum, which is usually large, to the base of the fifth metatarsal. It is in many cases a powerful abductor of the little toe. Peroneus Quarti Digiti.-This muscle is always present, and generally rises just above the fusion of the fibula with the tibia. It has the usual insertion. Peroneus Quinti Digiti.-This is quite constant and rises just above the last. Gastrocnemius. -The gastrocnemius differs in no respect from the description given of it in the other Rodents. The three Mole-rats Rhizomys, Georychus, and Bathyergus have no fabellae developed in the origin of the muscle, while in every other animal examined one was present in each head. Soleus.-The soleus rises from the back of the head of the fibula and joins the tendo Achillis just below the middle of the leg. In Myoxus, however, it rose from the middle of the fibula. The ropelike twisting of the tendo Achillis already referred to l is always evident. 1 Author's paper, Journ. Anat, vol. xxviii. p. 414. |