MARSUPIAL1A. 



283 



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 Dasyure& 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 ilia is 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, (Jig. 108,) which 



Fig. 108. 



The Marsupial bones (a, a, fig. 109) are 

 Fig. 109. 



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. 



Pelvis and marsupial bones i,f 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 

 femoris. 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.f 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 not in the females 

 of those animals which give birth to the smallest 



* See his note inserted in the ' Bulletin des Sci- 

 ences Medicales' of Ferussac, 1827, No. 77, p. 112, 

 and the Anuales d'Anat. et de Physiologic, 1839, 

 p. 240. 



t See the abstract of a paper on the anatomy of 

 the Dasyurus, Proc. Zool, Soc v January, 1835. 



