THE ABDOMEN. 235 



driac regions, superiorly placed to the diverging portion, it 

 increases in size and the number of its bands until it again 

 reaches the epigastric region, when it inclines backwards, 

 it attains its maximum calibre, and has three muscular 

 bands. After passing into the umbilical region it termi- 

 nates in the single colon, which has two muscular bands, 

 hangs freely in the free margin of the mesorectum, being 

 about three^ feet in length, until at the central line poste- 

 riorly it terminates in forming the rectum, which runs 

 directly from the posterior part of the hypogastric region 

 to the anus. Its muscular wall is very thick with the 

 fibres well marked; superiorly it is in contact with the 

 under surface of the sacrum and the structures about it ; 

 while its inferior surface, in the male, rests upon the upper 

 surface of the bladder, prostate, &c., and in the female 

 upon the vagina. In contact with its walls laterally is the 

 hypogastric plexus. Its muscular coat terminates poste- 

 riorly in forming the inner portion of sphincter ani, of 

 which the external portion is formed of dark-red fibres, 

 supplied with nerve-force hy the posterior part of the spinal 

 cord. To this muscle superiorly is attached levator ani, 

 running from the under part of the anterior coccygeal 

 bones. Laterally, retractor ani, from the inner surface of 

 the sacro-sciatic ligament, as far forward as the ileum ; 

 inferiorly, depressor ani, which, in the female, blends with 

 sphincter vaginae ; in the male with retractor penis. The 

 mucous membrane of the rectum is continuous posteriorly 

 with the thin, hairless skin, which is around the anus 

 " like the mouth of a draw-purse," and which has many 

 sebaceous glands. Some fat also enters into the formation 

 of the anus. The glands and villi of the mucous mem- 

 brane gradually decrease in number from the csecum to 

 the anus. 



The spleen is a peculiar sickle-shaped organ, attached to 

 the left extremity of the greater curvature of the stomach 

 by the gastro-splenic omentum. Of a bluish colour, and 

 about three pounds in weight ; it presents a base and an 

 apex^ a greater and a lesser curvature, and two surfaces. The 

 hase is attached up against the left kidney, and prerenal 

 capsule, and from this the organ extends in a downward and 

 backward direction and towards the right side, gradually de- 

 creasing in size. The lesser curvature, hilum, is that situated 

 nearest the stomach along which the vessels of the organ 



