440 



ABDOMEN 



and the sacrum and coccyx behind, and, when empty, it has 

 its anterior wall pressed against its posterior wall, and in that 

 condition its lumen appears, in transverse section, as a 

 transverse slit (Fig. 206). Behind the apex of the prostate, 

 where the gut bends to become the anal canal, its anterior 

 wall, in the distended condition, sometimes shows a slight 

 bulging cul-de-sac, called the ampulla recti, which descends to 

 a lower level than the prostate. 



Pars Analis Recti. The anal canal is the narrow slit-like 

 passage, about 38 mm. (one inch and a half) in length, which 

 leads from the rectum to the anal orifice. The canal com- 



Ureter 



Superior surface 



Seminal 

 vesicle 



Middle 

 umbilical 

 ligament 

 Infero-lateral surface 



Prostate 



Membranous urethra 



FIG. 207. Bladder, hardened in situ, viewed from the right side. 

 It contained a very small quantity of fluid. (A. F. Dixon. ) 



mences opposite the apex of the prostate, and proceeds 

 downwards and backwards. It is totally destitute of peri- 

 toneum, but it is clothed and supported by a prolongatioi 

 of the rectal layer of the pelvic fascia, which it pierces. Ii 

 addition, it is closely surrounded by strong muscles, whicl 

 keep close guard over it and allow its side-walls to separate 

 from each other only during defaecation. The muscles are : 

 the internal sphincter, developed from the circular muscle of 

 the gut and encircling the canal 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 sides of the canal near' its upper end, and pinch 

 in its walls. The membranous part of the urethra and the 

 bulb of the urethra are in front of the canal, but, on account 

 of the backward inclination of the gut, they are separated 

 from it by a mass of fibre-elastic tissue corresponding to the 



