THE INTESTINAL CANAL. 



1039 



marked anteriorly at the apex of the prostate, is the largest part, the ampulla 

 of the rectum. 



The lowest inch of the rectum, the anal canal, is an antero-posterior slit, the 

 lateral walls resting on each other (Fig. 658). In pathological cases the calibre 

 may be so distended as to occupy the 

 whole pelvis. 



The ilirsi-tioit of the rectum, starting 

 usually from the left of the base of the sa- 

 crum, is obliquely downward, backward, 

 and to the right. When it comes to the 

 level of the third sacral vertebra it has 

 reached themiddle line. It now passes that 

 line a little and runs along the right lat- 

 eral part of the fourth sacral vertebra. 

 It again returns to the middle line at 

 about the sacro-coccygeal junction and 

 passes downward and forward, and may 

 cross it a second time till it reaches the 

 level of a transverse line drawn between 

 the anterior parts of the ischial tuberos- 

 ities. This point is also opposite the 

 apex of the prostate gland (Fig. 657). 

 This point is not opposite the lower end 

 of the coccyx, as often stated, but fully 

 one inch below that. 



Sappey thus describes two lateral 

 curves, and, with two antero-posterior 

 curves, makes four altogether. The 

 first turn of the rectum from left to 

 right he does not consider a curve. The lateral curves are of little importance, 

 and run into each other. The first is the more pronounced, and corresponds to 

 the junction of the third and fourth pieces of the sacrum, with its concavity to 

 the left. The second corresponds to the sacro-coccygeal junction, with its con- 

 cavitv to the ri^ht. Thev are best seen with an emptv rectum, and are almost 



O / i v 



effaced when it is distended. 



The <tnt>-ro-]>,jxterior cun-e* are more pronounced and independent of the 

 degrees of dilatation. The first or sacral curve is due to the conformation of 

 the sacro-coccygeal column. It has its concavity forward, its convexity being 

 most marked at the junction of the third and fourth sacral vertebrae. The 

 second or perinc'il //>>' has its convexity forward, corresponding to the apex 

 of the prostate gland in the male and posterior wall of the vagina in the female. 

 Its concavity looks downward and backward. The sacral curve represents the 

 arc of a circle. The last one is angular. 



According to its direction, then, the rectum is divided into three parts a 

 superior portion, passing obliquely downward and backward : a middle portion 

 passing obliquely downward and forward ; an inferior or anal portion, passing 

 obliquely downward and backward. They are not of equal lengths : that of the 

 first is 8 to 9 cm. ; second. 10 to 11 cm. ; third, 2 to 3 cm. in the male, 1.5 to 

 2 cm. in the female. According to Quain, in order, the first part is five or four 

 inches ; second, three or four inches ; anal canal, one-half to one inch. In the 

 infant the rectum is straighter, less flexuous, and relatively larger than in the 

 adult. In the female it is said to be larger and straighter than in the male. 



The first, or superior, portion includes about half the length of the tube, and 

 extends obliquely from the pelvic brim, opposite either the left sacro-iliac artic- 

 ulation or the sacro-vertebral angle or the right side of the base of the sacrum, 

 to the body of the third sacral vertebra. It is almost completely surrounded 

 by peritoneum, which is connected to the anterior surface of the sacrum by the 



FIG. 658. Coronal section through the anal canal. 

 (Symington.) B. Cavity of bladder. VD. Vas deferens. 

 SV. Seminal vesicle. R. Second part of rectum. AC. 

 Anal canal. LA. Levator ani. 1*. Internal sphincter. 

 .?. External sphincter. 



