1672 



HUMAN ANATOMY. 



Blood-Vessels. — The arteries of the colon are derived from the superior and 

 the inferior mesenteric. The former supplies the caecum, the ascending and the 

 transverse colon, and a varying amount of the descending colon. The supply of the 

 latter is completed by the inferior mesenteric, which is also distributed to the sigmoid 

 flexure. The general plan includes a series of anastomoses between neighboring 

 branches, by which long arterial arches run near the border of the gut, to which 

 they give off irregular twigs. There is no system of straight vessels as in the greater 

 part of the small intestine. In the sigmoid flexure there is a recurrence of the 

 superimposed arches, which may be three in number. The superior hemorrhoidal 

 branch of the inferior mesenteric artery runs in the last part of the mesentery of the 

 sigmoid, and often divides in it into two branches, which run side by side on the 

 back of the gut towards the rectum. The veins are disposed much the same as 

 the arteries, but with a system of straight vessels from the intestine. 



The lymphatics, which are many, empty into lymph-nodes on the posterior 

 wall of the abdomen, which are a part of the same system as those of the small 

 intestine. 



The nerves are from the superior and inferior mesenteric plexuses, which are 

 derived chiefly from the solar and the aortic plexus respectively. 



THE RECTUM, ANAL CANAL, AND ANUS. 



The Rectum. — The rectum begins at the middle of the third sacral vertebra, 

 the point at which usually the mesentery that restrains the sigmoid flexure termi- 

 nates. It was formerly described as beginning at the left sacro-iliac joint, but this 

 division, which is unwarranted, has now become obsolete. The rectum descends 



Rectal folds 



Sacrococcygeal !^ 



articulation 



Hemorrhoidal vein 



Levator ani 



Bladder 



Seminal vesicle 

 Symphysis pubis 



External 

 sphincter 



Internal sphincter 



Veins of mucosa of anal canal \ 



Prostate 

 Veins 



Urethra 



Bulb of penis 

 Internal sphincter 

 Levator ani 



Fold of mucous membrane 



External sphincter 



Sagittal section of pelvis passing through rectum, anal canal, bladder, and urethra. 



along the hollow of the sacrum and coccyx, passes the point of the latter, and con- 

 tinues until it reaches the lower and back part of the prostate gland in the male or 

 the vagina in the female. Its length is about 12.5 cm. (approximately 5 in.). The 

 gut is then continued by the anal canal, sometimes called the sphincteric portion of 



