OF THE MARSUPIALIA. 403 
Of the Pelvic Extremities.—The pelvis in the mature Marsupial 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 Marsupit. 
We seek in vain for any relationship between the size of the pelvis and that of tne 
new-born young, the minuteness of which is so characteristic of the present tribe of 
animals. The diameters both of the area and the apertures of the pelvic canal are al- 
ways considerable, but more especially so in those Marsupialia which have the hinder 
extremities disproportionately large; as also in the Wombat, where the pelvis is re- 
markable for its width. The pelvis is relatively smallest in the Petaurists. The anterior 
bony arches formed by the ossa pubis and the ischia are always complete, and the inter- 
space 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 ila offer an elongated 
prismatic form ; they are straight in the Opossum, but gently curved outwards in the 
other marsupial genera. In the Dasyures there is a longitudinal groove, widening 
upwards, in place of the angle at the middle of the exterior surface of the ilium. 
The ilia in the Petaurists are simply compressed from side to side. They are broader 
and flatter in the Perameles, and their plane is turned outwards. But the most remark- 
able form of the ilia is seen in the Wombat, in which they are considerably bent out- 
wards at their anterior extremity. 
In the Kangaroos and Potoroos the eye is arrested by a strong process, given off from 
near the middle of the ileo-pubic ridge ; and this process may be observed less developed 
in the other Marsupialia. 
The tuberosity of the ischia inclines outwards in a very slight degree in the Dasyures, 
Opossums, Phalangers, Petaurists, and Perameles ; in a greater degree in the Kangaroos 
and Potoroos ; and gives off a distinct and strong obtuse process in the Wombat, which 
not only extends outwards, but is curved forwards. In the Potoroos the symphysis of 
the ischia, or the lower part of what is commonly called the symphysis pubis, is produced 
anteriorly. The length of this symphysis, and the straight line formed by the lower 
margin of the ischia, is a characteristic structure of the pelvis in most of the Marsupials. 
The marsupial bones are elongated, flattened, and more or less curved, expanded at 
the proximal extremity, which sometimes, as in the Wombat, is articulated to the pubis 
by two points ; they are relatively longest, straightest, and most slender in the Pera- 
meles ; flattest, broadest, and most curved in the Koala, and shortest in the Myrmeco- 
bius', where they do not exceed half an inch in length. They are always so long that 
'! The presence of these characteristic bones in the skeleton of the Myrmecobius exposes the fallacy of the 
doubts of its marsupial character entertained by some naturalists, as M. Gervais, who had not confidence in 
the marsupial modifications of the cranium pointed out in Mr. Waterhouse’s original description of this genus. 
