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Show 412 MR. ST. GEORGE MIVART AND DR. J. MURIE [June 26, and Rabbit (according to our dissections) this muscle has but a single head of origin, which arises from the upper portion of the tibia, thus differing widely from the condition present in the Agouti and Guinea-pig- Meckel * says that in the Porcupine it is united with the extensor prnprius hallucis; but in our specimen that muscle existed in addition to the double tibialis anticus. He further observes-)- that in the Marmot the tibialis anticus is divided into a large tibial and a small peroneal head ; but there is no mention of any origin from the femur. The extensor longus digitorum arises by a very broad tendon from the femur, just external to the long tendon above-mentioned of the tibialis anticus. Proceeding downwards, it divides into three tendons, which are respectively inserted into the second phalanges of the only digits present, i. e. second, third, and fourth (figs. 4 & 5, E. I. d.). The Guinea-pig appears to have a similar disposition in this muscle, although in one foot we noticed the inner tendon bifurcating, the double tendon going to the same digit. In the Hare and the Rabbit it arises by a long, round (instead of flattened), strong tendon from the front of the outer condyle of the femur; this tendon then runs through that groove which the femoral tendon of the tibialis anticus traverses in the Agouti. It divides into four tendons, which are inserted into the four digits ; that to the index or inner toe sends a branch to the third digit. The extensor proprius hallucis is rather a delicate muscle (fig. 5, E.p. h.). It arises from the upper two-thirds of the fibula and interosseous membrane, gives origin to a slender tendon, which ends in an insertion into the second phalanx of the index. The same in Guinea-pig. This muscle is absent in the Hare and Rabbit. The muscular fibres of the extensor brevis digitorum extend forwards over about the posterior third of the metatarsal bones, arising also from the dorsum of the tarsus above the cuboid and os calcis. These give rise to two tendons, which are inserted respectively into the two inner toes, namely the index and third digits, joining at the side the tendons of the long extensors. It is the same in the Guinea-pig ; but this muscle is wanting in the Hare and Rabbit. Peroneus longus. This is a small muscle arising, as in Hyrax%, from the head of the fibula, on each side of the lateral ligament, so that at first sight it appears as if it arose by a tendon from the femur, like the extensor longus digitorum. Passing down behind the external malleolus it sinks beneath the foot, passing through the groove on the outer side of the cuboid, crosses the sole deeply (hidden by * Loc. cit. p. 410. t Ibid. p. 411. X See P. Z. S. 1865, p. 348, and fig. 12. p. 349, where, by an error of the artist (pardonable by reason of the very deceptive appearance of the external lateral ligament), the peroneus longus has been figured as if arising by tendon from the femur, which, as may be seen in the description, it does not; while the extensor longus digitorum, which really does arise from the femur, is represented as coming only from the tibia. |