SKELETON OF MARSUPIALIA. 355 



like a thumb, all the fingers enjoy lateral motion, and that 

 those at the outer can be opposed to those at the inner side so 

 as to grasp an object and perform, in a secondary degree, the 

 function of a hand. In the Koala the two inner dimts are more 

 decidedly opposed to the three outer ones than in any other 

 climbing Marsupial. But some of the Phalangers, as the Ph. 

 Cookii and Ph. gliriformis of Bell, present in a slighter degree 

 the same disposition of the fingers, by which two out of the five 

 have the opposable properties of a thumb. I have observed a 

 similar disposition of the digits in the act of climbing in the 

 Dormouse, and it probably is not uncommon in other placental 

 Mammalia of similar habits and which have long, slender, and 

 freely moveable fingers. As a permanent disposition of the digits, 

 the opposition of three to two is most conspicuous in the prehensile 

 extremities of the Chameleon. 



The pelvis, figs. 152, 226, 227, in the mature Marsupials is 

 composed of the os sacrum, the two ossa innominata, and the 

 characteristic supplemental bones, attached to the pubis, called 

 by Tyson the ossa marsupialia or Janitores Marsupii, m. 



We seek in vain for any relationship between the size of the 

 pelvis and that of the new-born young, the minuteness of which 

 is so characteristic of the present tribe of animals. The diameters 

 both of the area and apertures of the pehdc canal are always con- 

 siderable, but more especially so in those Marsupialia which have 

 the hinder extremities disproportionately large ; as also in the 

 Wombat, where the pehis is remarkable for its width. The 

 pelvis is relatively smallest in the Petaurists ; but even here the 

 diameter of the outlet is at least six times that of the head of the 

 new-born young. The anterior bony arches formed by the ossa 

 pubis and the ischia are always complete, and the interspace 

 between these arches is divided, as in other Mammalia, into the 

 two obturator foramina by an osseous bridge continued from the 

 pubis to the ischium on each side of the symphysis. 



In the Kangaroos, Potoroos, Phalangers, and Opossums, the 

 ilia offer an elongated prismatic form. They are straight in the 

 Opossum, but gently curved outward in the other Marsupial 

 genera. In the Dasyures there is a longitudinal groove Avidening 

 upward in place of the angle at the middle of the exterior sur- 

 face of the ilium. The ilia in the Petaurists are simply compressed, 

 with an almost trenchant anterior margin. They are broader and 

 flatter in the Perameles, and their plane is turned outward. But 

 the most remarkable form of the ilia is seen in the Wombat, in which 

 they are considerably bent outward at their anterior extremity, 



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