MARSUPIALIA. 
the pubis to the ischium on each side of the 
symphysis. 
In the Kangaroos, Potoroos, Phalangers, and 
Opossums the ilia offer an elongated pris- 
matic form. They are straight in the Opossum, 
but gently curved outwards in the other Mar- 
supial genera. In the Dasyures there is a lon- 
gitudinal 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, with an almost trenchant 
anterior margin. They are broader and flatter 
in the Perameles, and their plane is turned 
outwards. But the most remarkable form 
of the iliais seen in the Wombat, in which 
they are considerably bent outwards at their 
anterior extremity. In the Kangaroos and 
Potoroos the eye is arrested by a strong pro- 
cess given off from near the middle of the 
ileo-pubic ridge, and this process may be ob- 
served less developed in the other Marsupialia. 
The tuberosity of the ischia inclines outwards 
in a very slight degree in the Dasyures, Opos- 
sums, Phalangers, Petaurists, and Perameles, 
in a greater degree in the Kangaroos and Poto- 
roos, and gives off a distinct and strong obtuse 
process in the Wombat, (fig. 108,) which 
Right os innominatum and marsupial bone, 
Wombat. 
not only extends outwards but is curved for- 
wards. In the Potoroos the symphysis of the 
ischia, or the lower part of what is commonly 
called the symphysis pubis, is produced ante- 
riorly. 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. 
283 
The Marsupial bones (a, a, fig. 109) are 
Fig. 109. 
(Mp 
ip 
Pelvis and marsupial bones of the Koala. 
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 
straightest and most slender in the Perameles ; 
shortest in the Myrmecobius, where they do 
not exceed half an inch in length; longest, 
flattest, broadest, and most curved in the 
Koala, where they nearly equal the iliac bones 
in size. They are always so long that the 
cremaster muscle winds round them in its 
passage to the testicle or mammary gland, and 
the uses of these bones will be described in 
treating of that muscle. 
With reference to the interesting question— 
What is the homology or essential nature of 
the ossa marsupialia? I entirely concur in the 
opinion first advanced by the able anatomist, 
M. Laurent,* viz. that they belong to the 
category of the trochlear ossicles, commonly 
called sesamoid, and are developed in the 
tendon of the external oblique which forms the 
mesial pillar of the abdominal ring, as the pa- 
tella is developed in the tendon of the rectus 
Jemoris. I had arrived at this conclusion from 
independent researches, and unaware of any 
prior announcement of this view when I dis- 
cussed the question before the Zoological So- 
ciety in 1835.+ I cannot, however, participate 
in the opinion of M. Laurent and the celebrated 
De Blainville, that the marsupial bones are 
superadded to the abdominal muscles to aid in 
an unusually energetic compression required to 
expel the uterine foetus. It is notin the females 
of those animals which give birth to the smallest 
* See his note inserted in the ‘Bulletin des Sci- 
ences Médicales’ of Férussac, 1827, No. 77, p. 112, 
and the Annales d’Anat. et de Physiologie, 1839, 
. 240. 
R + See the abstract of a paper on the anatomy of 
the Dasyurus, Proc. Zool, Soc., January, 1835. 
