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 Bathy- 
ergus 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, 
Heleromys, Mus barbarus and M. rattus. In Georychus the fourth 
toe has aslip as well. In Myoxus and Bathyergus I 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 faras 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 Bathyerqus have no fabellz 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 
Mypoxus, however, it rose from the middle of the fibula. The rope- 
like twisting of the tendo Achillis already referred to’ is always 
evident. 
? Author’s paper, Journ. Anat, vol, xxviii. p. 414. 
