102 Proceedings of tJte Royal Society of Victoria. 



of the inner surface of the thigh and leg. The relations of these 

 vessels in the leg and foot appear to be normal. On the inner 

 surface of the common iliac artery and opposite to or above — 

 but so far as my observations go, never below — the origin of the 

 external circumflex, there is given off on each side, a very large 

 internal iliac artery (/./.). This is often as large as the external 

 iliac artery. It sometimes arises almost dorsally from the common 

 iliac artery, but whether so or not, always runs at tirst deeply 

 and almost vertically upwards towards the dorsal surface of the 

 animal, among the muscles of the pelvis. So sharply does it 

 turn upwards, that, in dissecting from the ventral surface, it often 

 appears to be absent, and is only to be seen on pushing over the 

 main external iliac artery outwards. Often one side or the other 

 has a much larger internal iliac artery than the opposite side, 

 and, when this is the case, a small vessel can with care be seen 

 connecting the two internal arteries. At tirst this artery gives 

 oft" no branches, but then sends off" a median sized one, pi-obably 

 the representative of the gluteal artery (^./.) from its outer side. 

 This branch appears to run almost vertically upwai-ds to pierce 

 the bony roof of the pelvis, and lose itself among the muscles of 

 this dorsal region, including the " ischiotergal" slip. The internal 

 iliac artery then passes backwards dorsally to the inner wall of 

 the acetabulum giving rise on its outer face to two or thi'ee 

 vessels, one of which is much larger than the others, which form 

 by their anastomoses a plexus which is embedded in fatty 

 tissue. From this plexus there arise two vessels running 

 forwards and outwards to supply the muscles, ventral and lateral 

 to the ankylosed metapophyses forming the dorsal wall of the 

 pelvis. The largest and posterior of the three runs outwards and 

 backwards (s.c), and from its relations to the sciatic nerves, to 

 the sacro-sciatic foramen, as well as its distribution to the 

 muscles of the back of the thigh, probably corresponds to the 

 sciatic artery of higher forms. The main trunk of the internal iliac 

 artery passes directly backwards as the lateral sacral artery (/.s.), 

 ventral to the transverse processes of the vertebrae, and supplies 

 the pyriform and coccygeal muscles of this region. Just below 

 the internal iliac artery there are given off" two somewhat small 

 vessels from the external iliac trunk, which correspond, the first 

 with the superior vesical branch (s.v.) given off' in Man from the 



