1896i] MYOLOGY OF nODENTS. 181 



Extensor Longus Digitorum. — As in all other Eodents, this muscle 

 rises by tendon from the front of the external condyle of the 

 femur. In 3Ius barharus, however, as in Sjphingurus and Dipun, 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 

 barbarics, 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 Projirius Hallucis.—'Jl\i\s 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 Qerhillus, Myoams, Mus barbarns, Georyclms, and Bathy- 

 ergus it rises from the second quarter of the fibula ; in Criceiomys, 

 Cricetus, and Mits rattus from the third quarter; in SJiizomys, 

 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, Cricel/us, Gerbillvs, llhizomys, Microtus, 

 Heteromys, Mus harbarus and M. ratt^ls, In Oeorycliug the fourth 

 toe has u slip ns well. In Myoxus and Bathyergusl was interested 

 to find a distinct but small tendon to the proximal phalanx of the 

 first toe, these being the only Rodents in «]iich 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 qnarti 

 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 difiers in no respect from 

 the description given of it in the other Rodents. The three Mole- 

 rats Rhizomys, Georychus, and Bathyergus have no fabellse 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 AchUlis just below the middle of the leg. In 

 Myoxus, 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, Joiirn. Anat, vol. xxviii. p. 414. 



