182 MR. r. G. PAKSONS ON THE [Jan. 14, 



Planiaris. — This has the typical rodent arrangement, the only 

 point of interest being the extent to which the muscular fibres of 

 tlie flexor brevis digit onim are developed in the sole. In Gerhillus 

 three little slips of muscle are alone seen in the intervals between 

 the four tendens where they first separate. In Mierotus the flexor 

 brevis has no muscular fibres at all, while in Myoxus and Myodes 

 there are very few. All the other animals examined had well- 

 developed muscnlar bellies to the flexor brevis. 



Popliteus. — The popliteus always rises from the external condyle, 

 and is inserted into the upper part of the internal border of the 

 tibia. 



Flexor Longus Hallucis {Flexor Fihularis). — This is always a 

 large mnscle, rising from both the tibia and fibula and being 

 inserted into the distal phalanges of all the toes. 



Flexor Longus Digitorum {Plexor Tibialis). — Dobson ' states that 

 this muscle in the Myomorpha is always separate from the flexor 

 fihularis tendon in the sole. I have, however, met with two 

 remarkable exceptions to this generalization, viz. Rhizomys and 

 Heteromys. In both of these animals the tendons unite in the sole 

 exactly as they do in the Hystricomorpha. I should mention that 

 this arrangement was present in both the right and left feet. In 

 Georychus and Bathyergus the muscle is better developed than in 

 most of the Myomorpha, and ends in a bone beneath the base of 

 the first metatarsal which I am inclined to regard as a rudiment of 

 a prsshallux. In all the other animals examined the muscle ends 

 chiefly in the fascia of the foot. 



Tibialis Posticus. — This is always a small muscle and rises from 

 the upper part of the posterior surface of the tibia below the 

 attachment of the popliteus, and also very often from the back of 

 the head of the fibula. As a rule it has a groove of its own behind 

 the internal malleolus, but in Myoxus it shares the groove of the 

 flexor fihularis. It is inserted into the under surface of the navi- 

 cular, though in Mus rattus it goes chiefly to the plantar fascia. 



Muscles of the Foot. 



Lumbricales. — InOeorychus, Bathyergus, Rhizomys, and Heteromys 

 only three lumbricales are present. All the other animals dissected 

 have four. 



Accessoriiis. — This muscle is very ill-developed in the Myo- 

 morpha. The only animal in whicli I found it really well marked 

 was in Bathyergus, although traces of it could be made out in Mus 

 rattus. 



Abductor Hallucis. — This is usually present and rises from the 

 navicular in Cricetomys, Rhizomys, Mus barbanis, and M. rattus. 

 In Oerbillus, Cricetus, Mierotus, Myo.vus, Heteromys, and OeorycJius 

 it came from the internal cuneiform. In Bathyergus it was well- 

 marked and rose from the sustenaculum tali of the enlcaneum, 

 its proximal part forming the calcaneo-scaphoid ligament. 



Journ. Aoat, xvii. p. 142. 



