Anatomy of Notoryctes tyi^hlcps. 101 



liepatic branches, and somewhat lower, a much larger vessel 

 the superior mesenteric artery, which gives off a distinct 

 inferior mesenteric artery to the lower parts of the intestine. 

 Below these are the renal arteries (Fig. 8, r.a.)^ the right being 

 small and short, the left long and broad. The spermatic arteries 

 {g.a.) are very small. Near and posterior to the renal arteries, 

 as so often in Marsupials, the aorta lies quite dorsal to the 

 posterior vena cava, by which it is coujpletely hidden, until 

 some distance below its bifurcation, when the external iliac 

 arteries come to lie, still somewhat dorsaily but more to the 

 outer side of the external iliac veins. From the following 

 description it will be seen that there is a great difference be- 

 tween this region in Notorcytes and in the Marsupial type, in 

 which the abdominal aorta, after giving off the external iliac 

 arteries, continues back, giving off the two internal iliac arteries, 

 the small continuation then forming the median sacral artery, 

 e.x'-i in the Kangaroo' and Ohoeropus.'^ In Notoryctes we find 

 that the aorta bifurcates to form the common iliac arteries 

 {c.c), and in front of this bifurcation, from the dorsal wall of the 

 aorta we may get a very small median sacral artery (^m.s.), often 

 only to be found by removing the neighbouring tissues, staining 

 and examining them vinder the compound microscope. At 

 other times I have found two, or in one case, three vessels, just 

 visible to the naked eye, arising on either side, posteriorly, of the 

 bifurcation, which from their distribution must represent the 

 median sacral artery. At other times I was unable to detect 

 any median sacral artery whatever. On its outer side each 

 common iliac artery gives off what correspond in their distribu- 

 tion to the ilio-lumbar arteries (/./.), and still further down there 

 arises the circumflex (<r.) artery, supplying the muscles of the 

 abdominal wall, and the external circumflex (e.c), a large vessel 

 with ascending and descending branches supplying the muscles 

 of the thigh. At about the middle of the thigh the external 

 iliac or femoral artery divides into (1) the deep or profunda 

 branch (t/.f.), which sends off a large twig, apparently the 

 superior perforating branch, to the muscles on the outer surface 

 of the thigh, and (2) the superficial femoral (s.f.) to the muscles 



1 Owen : Anatomy of Vertebrates, vol. iil., p. 540. 



2 Parsons: Jour. Linn. Soc. Lond., vol. .\xlx., Oct , 1003, p. 64. 



