ORDER CARNASSIER. 13 



nates. We know that the aorta is always divided at the sum- 

 mit of the crest of the iliac bones. As the pelvis is longer in the 

 Marsupiata, this circumstance places the termination of the 

 aorta higher up. The iliac branches in descending form a 

 more acute angle, and for this reason the blood is more 

 drawn into the principal branch extending even into the 

 crural artery. A third branch, equally great in calibre, is 

 that of the middle sacrum. From this results the powerful 

 and prehensile tail of the didelphes. 



In man the primitive iliac is divided into two trunks, 

 which, from the very near equality of their volume, have 

 been considered the same, and called secondary iliacs. 

 These are the external and the internal. The internal iliac 

 becomes the hypogastric, after having furnished a tolerably 

 strong branch, the ileo-lumbar. Its volume is but little 

 diminished by this, so that the hypogastric remains a pow- 

 erful trunk, of large calibre, and in which is involved a vast 

 mass of nutritious fluids. 



It is quite different with the marsupiata. As the primitive 

 iliacs spring more high, it follows that the crural artery in 

 parting from the primitive iliac forms a mother- branch, 

 which has but very small branches on the sides. The first 

 which present themselves, and which spring exactly from 

 the same point, one to the right, and the other to the left, " 

 are the ileo-lumbar without, and the hypogastric within. 

 There is a striking analogy between these two arteries, from 

 the distribution of their branches, but more especially from 

 the equality of their volume. Thus the hypogastric, so large 

 in man, that it is one of the two bifurcations of the primi- 

 tive iliac, and is thus the congener of the crural, is very 

 limited in the marsupiata. Now the uterine and vaginal 

 arteries are derived, as is well known, from the hypogastric. 



The uterine and vaginal arteries, which are but small 

 branches of the hypogastric, supply capillary tops to their 

 organs. Diminished as they are in calibre, though suffi- 



