288 me. f. g. pabsosts ox the [Mar. 20, 



the internal condyle. (3) A slip rising behind this by a very thin 

 tendon from the same origin and running to the middle third of 

 the posterior border of the femur. These three probably represent 

 the adductors longus and brevis. (4) A slip from the tuber ischii 

 running obliquely across the leg to above the internal condyle and 

 also to the posterior surface of the femur above it. This is supplied 

 by the great sciatic nerve instead of the obturator, and is the second 

 part of the semimembranosus joined to the adductors. (5) A 

 massive muscular slip from -the outer side of the tuber ischii to 

 the upper part of the shaft of the femur. In Spermophihu, Xerus, 

 Arctomys, and Castor the arrangement is essentially the same, but 

 in Pteromys an extra deep slip was observed running behind the 

 obturator nerve to the upper part of the femur, while the portion 

 described as ]Sb. 4 in Sciurus had a much more extensive attach- 

 ment up the femur. Meckel describes five heads in Arctomys. In 

 Castor, although the arrangement is identical with that of Sciurus, 

 the muscle is very massive and the separate parts much less easy 

 to identify. 



Tibialis Anticus. — This muscle usually rises from the upper part 

 of the outer surface of the tibia, and is inserted into the internal 

 cuneiform and first metatarsal by two slips. In those cases in 

 which the halux is absent or rudimentary the tendon does not 

 divide into two at its insertion. 



In Dvpus cegyptius its insertion is into the inner side of the base 

 of the great metatarsal bone. 



Among the Octodontidae, Myopotamus and Capromys have a 

 double insertion, Aulacodus and Octodon a single one. In the 

 Hystricidse it has a double insertion (Bystrica, Sphingumg, Erethizon). 

 Meckel 1 says that in ffystrix it is blended with the extensor pro- 

 prius hallucis; but this 1 did not find. In the Chinchillida? it not 

 only rises from the tibia but from the tendon of origin of the ex- 

 tensor longus digitorum (Chinchilla, Lagostomus). 



In the DasyproctidaB it rises from the front of the external 

 condyle of the femur by a tendon which is anterior to that of the 

 extensor longus digitorum, as well as by fleshy fibres from the upper 

 part of the tibia ; it is inserted by a single tendon, which in Dasy- 

 'procta goes to the base of the internal (2nd) metacarpal, and in 

 Ccelogenys to the internal cuneiform. In the Caviidae it has the same 

 origin as in the Chinchillidse, and is inserted into the rudimentary 

 fused internal cuneiform and first metatarsal, which is found under 

 the base of the internal (2nd) metatarsal. 



Mivart and Murie* found a femoral origin, as in the Dasyproctidae, 

 in some of the Guinea-pigs they dissected. Beddard 3 describes 

 the same arrangement in Dolichotig patagonica. 



In three Guinea-pigs I have not found a femoral origin once, and 

 the specimen of Ceredon rupestris I dissected did not show it. I 

 also did not see it in D. patagonica. Further observation is needed 



1 Op. cit. p. 410. 



2 P. Z. S. 186fi, p. 383. 



3 P. Z. S. 1891, p. 236. 



