MARSUPIALIA. 



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 polticis, 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 commu- 

 nis longus ; 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 (Jig. 113) of this 

 modification of the muscles of the hind-foot is 

 taken from a dissection of the Pkalangista vul- 

 pina, which very closely accords with that 

 above described in the Duxyurus macrurus: a, 

 expanded tendon of the sartorius; b, gracilis ; 

 c, Semite ndinosus ; and d, semi-membranosus ; 

 both these muscles are inserted, as in many 

 other quadrupeds, low down the tibia : e, gas- 

 trocnemius ; J\ plantaris; g, the analogue of 

 the flexor longus pollicis pedis ; h, tibialis posti- 

 cus ; this muscle divides and is inserted by two 

 tendons, A' and //', into the internal and middle 

 cuneiform bones : t, 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. 



* Zoolog. Proceedings, 1830, p. 59. 



Fig. 113. 



SJuscies of leg, Phalung'uila vvlp'ui 



NERVOUS SYSTEM. 



The brain bears a smaller proportion to the 

 body in the Marsupials than in any other order 

 of Mammals : thus, in the Ursine Dasyure it 

 is as 1 to 520, in the Wombat as 1 to 614, 

 in the great Kangaroo as 1 to 800 : it is 

 relatively largest in the smaller species of 

 Petaurists and Phalangers. 



The Marsupial brain is also the simplest as 

 respects its external form in the Mammiferous 

 class. The cerebral hemispheres do not ex- 

 tend over the cerebellum in any of the species, 

 and in some, as the Dasyures and Opossums, 

 they leave the optic lobes exposed. The brain 

 consists, as in other Mammalia, of a medulla 

 oblongata with a pons Varolii, cerebellum 

 (d,Jig. 114), optic lobes, or bigeminal bodies, 

 (c, fig. 114), cerebrum (6), to which may be 

 added, on account of their large proportional 

 size and distinct development, the olfactory 

 lobes (a, a,). In the Phalangers and Petau- 

 rists, the Opossums, Perameles, the insectivo- 

 rous Phascogales, and the smaller Dasyures the 

 surface of the cerebral hemispheres is smooth 

 and unconvoluted. In the iDasyurus ursimis 

 the complication of the cerebral surface is 

 merely indicated by a few slight indentations ; 

 it is in the strictly herbivorous species as the 

 Kangaroo (jig- 115) and Wombat, that the 



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