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Show 288 MR. F. G. PARSONS ON 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 Spermophilus, 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 No. 4 in Sciurus had a much more extensive attachment up the femur. Meckel describes five heads in Arctomys. In Castor, although the arrangement is identical wdth 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 Dipus 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 Hystricidae it has a double insertion (Hystrix, Sphingurus, Erethizon). Meckel1 says that in Hystrix it is blended with the extensor pro-prius hallucis ; but this I did not find. In the Chinchillidae it not only rises from the tibia but from the tendon of origin of the extensor longus digitorum (Chinchilla, Lagostomus). In the Dasyproctidae 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 Dasyprocta 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 Chinchillidae, 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 Murie2 found a femoral origin, as in the Dasyproctidae, in some of the Guiuea-pigs they dissected. Beddard3 describes the same arrangement in Dolichotis 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. 1866, p. 383. 3 P. Z. S. 1891, p. 236. |