194 ANATOMY OF THE RABBIT. 
colon (anastomosing with the middle colic), and the superior 
haemorrhoidal artery (a. haemorrhoidalis superior) to the 
posterior portion of the colon and the rectum. 
9g. The superior mesenteric vein (v. mesenterica superior), 
the chief tributary of the portal, collects the blood distributed by 
the superior mesenteric artery, its tributaries being similar in 
arrangement to the branches of the artery. The inferior mesen- 
teric vein (v. mesenterica inferior) collects blood from the de- 
scending colon and rectum; it may be traced forward in the descend- 
ing mesocolon. 
10. Sympathetic plexuses. In the descending mesocolon will be 
found the inferior mesenteric ganglion (g. mesentericum in- 
ferius), a narrow curved body situated in front of the inferior 
mesenteric artery. Surrounding the abdominal aorta and appear- 
ing in the mesocolon is the abdominal aortic plexus (plexus 
aorticus abdominalis). It is connected anteriorly with the coeliac 
and superior mesenteric plexuses (p. 183) accompanying the corres- 
ponding vessels, and with the renal plexuses accompanying the 
renal vessels to the kidneys; posteriorly with the inferior mesen- 
teric and spermatic plexuses about the inferior mesenteric 
and internal spermatic arteries, and with the hypogastric plexus 
about the pelvic vessels. 
11. By dividing the rectum close in front of the pelvis, and 
severing the peritoneal attachments, the intestines may be separ- 
ated and laid out in an extended condition. The relations to one 
another of the ileum, caecum, and colon are studied to much better 
advantage than in the natural position. 
VI. THE URINOGENITAL SYSTEM. 
(For the general relations of the urinogenital organs, see p. 92). 
A. The Urinary Organs. 
The central organs of excretion, the kidneys (renes), occupy an 
anterior position on the dorsal wall of the abdomen. The right 
kidney is placed a little farther forward than the left, and is largely 
covered by the right posterior lobule of the liver. In addition to a 
fibrous coat immediately surrounding the kidney substance, each 
organ is imbedded in a mass of fatty material, the adipose capsule 
