The reetus femoris has its two origins very distinct, and its analogy to the biceps of the upper extremity is very close. The grucilis is a very thick and strong muscle.
The biceps flexor cruris in the Perameles is a muscle of very great strength ; it terminates in a strong and broad aponeurosis, which ex tends over the whole anterior part of the tibia, being attached to the rotular tuberosity of that hone, and terminating below in the sheath of the tendo Achillis, whereby this muscle be comes an extensor of the foot.
It is a curious fact that all the equipedal Marsupials, whether burrowers as the Wom bat, climbers as the Koala, Phalangers, and Opossums, or simply gressorial, as the Da syuride, have the tibia and fibula so connected together as to allow of a certain degree of ro tation upon each other, analogous to the pro natory and supinatory movements of the bones of the antibrachium, and the muscles of the leg present corresponding modifications. It is not without interest in the question of the affinities of the Marsupials to find that none of the analogous carnivorous, pedimanous, or rodent Placentals present this condition of the hind leg.
In the Dasyurus macrurus, the plantaris. instead of rising from the femur, has its fixed point in the fibula, from the head to half-way down the bone, fleshy ; its tendon passes ob liquely inwards and glides behind the inner malleolus to its insertion in the plantar fascia, so that it rotates the tibia inwards besides ex tending the foot. The soleus has an extensive origin from the proximal to near the distal end of the fibula. There are as usual three deep seated muscles at the back of the leg. Of these three the muscle analogous to the tibialis postieus is readily recognized; its tendon glides behind the inner malleolus, and is inserted into the inner or tibial cuneiform bone.
The muscle which has the relative position and origins of the flexor longus pollicis, sends its tendon by the usual route to the sole of the foot, where it divides and distributes a flexor tendon to all the toes except the rudimental hallux ; it has the same disposition in the Opossums, where the hinder thumb or great toe is fully developed; for this modification, however, the Comparative Anatomist is already prepared by meeting with it in the first step from man, viz. in the Chimpanzee and Orang.* The third deep-seated muscle, being situ ated internal to the two preceding ones, may be the analogue of the flexor digitorum COMMIS nis bongos; it nevertheless sends no tendon to the toes nor even to the tarsus, but its fibres pass from the tibia obliquely outwards and down wards between the preceding muscle and the interosseous ligament to the fibula, where they are exclusively inserted so as to oppose the plantaris and rotate the foot outwards. This
muscle closely adheres to the interosseous fascia, and thus resembles in its attachments the pronator quadratus of the fore limb : it is most developed in the pedimanous climbing Marsupials, where the rotation of the foot is more extensive and more useful.
The subjoined illustration (fig. 113) of this modification of the muscles of the hind-foot is taken from a dissection of the Phalangista vul pina, which very closely accords with that above described in the Dasyurus rnacrurus: a, expanded tendon of the sartorius; b, gracilis ; c, setnitendinosus ; and d, semi-membranosus ; both these muscles are inserted, as in many other quadrupeds, low down the tibia : e, gas trocnemius ; f, plantaris ; g, the analogue of the flexor bongos pollicis pedis; h, tibialis posti cus ; this muscle divides and is inserted by two tendons, and Is", into the internal and middle cuneiform bones : i, the rotator muscle of the tibia, probably a modification of the flexor digitorum communis pedis ; its fibres descend obliquely from the fibula p to the tibia t.
In the muscles on the anterior part of the leg I observed no peculiarity worthy of notice; the extensor brevis digitorum has, however, its origin extended into this region and is attached to the outside of the fibula. There are three peronei ; the external one is inserted into the proximal end of the fifth metatarsal : the ten don of the middle peroneus crosses the sole in a groove of the cuboid like the peroneus longus: the internal peroneus is an extensor of the outer or fifth toe. The Perameles lagotis, among the Saltatorial Marsupials, presents a different condition of the extensors of the foot from that above described. The gastrocnemii, soleus, and plantaris all arise above the knee joint, and the tendon of the plantaris, after sheathing the tendo Achillis and traversing the long sole, is finally inserted into the base of the metatarsal bone of the fourth or largest toe ; thus this muscle, which is strongly de veloped, bends both this toe and the knee, while it extends the foot.