PELVIS 



585 



to the anal orifice. The canal commences at the apex of 

 the prostate and proceeds downwards and backwards. It is 

 totally destitute of peritoneum, but it is clothed and supported 

 by a prolongation of the rectal layer of the pelvic fascia 

 which it pierces. In addition, it is closely surrounded by 



Anal canal (note the| (( 

 apposition of its lateral; 



walls)^ JjJI 



Sphincter ani internus-^ 



t'Jlftl 



Sphincter ani externus \ N N // /f 



FIG. 231. Coronal section through the whole length of the Anal Canal. 

 (Symington.) 



B. Bladder. R. Terminal portion of the rectum 



V.D. Ductus deferens. (note the apposition of its an- 



S.V. Seminal vesicle. terior and posterior walls). 



strong muscles, which keep close guard over it and allow 

 its lateral walls to separate from each other only during 

 defalcation. The muscles are : the internal sphincter, developed 

 from the circular muscle of the gut and encircling it in nearly 

 its whole length ; the external sphincter which surrounds the 

 lower orifice and lower part of the wall; the levatores ani, 

 whose medial margins grasp the canal laterally, near its 



