DISSECTING MANUAL. 



the pelvic floor and becomes the anal canal. It lies on the sa- 

 crum, coccyx, and pelvic floor, following their curves, and also 

 curves laterally in (usually) three flexures, the upper and lower 

 being concave to the left, and the middle one to the right. 

 External creases mark these flexures, which produce, inside the 

 gut, lateral crescentic shelves (rectal valves) . At its lower end 

 is a special enlargement (rectal ampulla). Peritoneum covers 

 only the upper two- thirds, at first in front of and at the sides, 

 later on in front only, and is then reflected at a point one inch 

 above the prostate, or three inches above the anus. [1087] 



Anal Canal. This is an inch to an inch and a half long, 

 quite narrow, and runs downward and backward to the exter- 

 nal orifice (anus) ; it is surrounded by the Sphincters and 

 (above) edges of the Levatores ani. It lies close behind the 

 bulb of the urethra (or perineal body). Its circular fibres are 

 greatly thickened in its upper inch, forming the Internal 

 sphincter. On the upper half of its mucous membrane are 

 from five to ten permanent vertical folds (columns of Mor- 

 gagni) ; these are connected at their lower ends by semilunar 

 folds (anal valves) which form pockets (sinuses). [1091] 



Liver. This lies under the diaphragm, on the right side and 

 extending to the left. Its position is sufficiently outlined by 

 lines connecting the following points, viz.: half an inch below 

 the right nipple; half an inch below the tip of the tenth right 

 rib; an inch below the left nipple. It has two surfaces, 

 parietal and visceral, separated by the inferior margin; and 

 consists of two main lobes, right and left, with three secondary 

 ones, quadrate, caudate, and Spigelian. Peritoneum covers it 

 entirely except the " uncovered area " on the right lobe (a small 

 triangular area on the posterior parietal surface), under the 

 falciform ligament, and (usually) the fossa of the gall bladder; 

 the lesser sac covers the caudate and Spigelian lobes only, the 

 rest being covered by the greater sac. [1108] 



The parietal surface is convex, adapted to the shape of the 

 diaphragm, and divided, according to position, into four areas. 



222 I 



