APPLIED ANATOMY. 



THE PELVIC VISCERA. 



RECTUM AND ANAL CANAL. 



The rectum extends from the level of the third sacral vertebra to where it 

 pierces the levator ani muscle, 3. 7 cm. ( i J^ in. ) in front of the tip of the coccyx, 

 but at a lower level, and opposite the lower and anterior part of the prostate. It is 

 8.75 cm. (3^ in.) long and passes into the anal canal ; this latter is 2.5 to 4 cm. 

 (i to i^ in.) long, and extends to the skin border (Fig. 445). 



When collapsed the rectum appears as a nearly straight tube following the curve 

 of the sacrum, but when distended it becomes distinctly sacculated It possesses an 

 external longitudinal and internal circular layer of muscular fibres. The longitudinal 

 fibres are continuous with those on the colon but instead of being composed of three 



Rectovesical pouch 



Seminal vesicles 



Prostate gland 

 Recto-urethralis muscle 



Valves of Houston 



Ampulla 



Columns of Morgagni 

 Internal sphincter 



External sphincter 



Crypts of Morgagni 



\ Compressor urethrae muscle 

 with Cowper's gland enclosed 



FIG. 445. Rectum and anal canal. 



bands are fused together into two bands, anterior and posterior. On the sides the 

 longitudinal fibres are not -so abundant. The circular fibres are continuous on the 

 anal canal as the internal sphincter. For the distance of 4 cm. ( i y^ in. ) between 

 the tip of the coccyx and its termination, the rectum lies on the two levator ani 

 muscles, which join in the median line. The lower portion of the rectum is larger 

 than the upper and is called the ampulla. 



The anterior surface of the rectum at the ampulla lies against the posterior sur- 

 face of the prostate but is not intimately adherent to it. At the apex of the prostate 

 the anterior rectal wall makes a more or less sharp turn backward. At this part the 

 rectum and the prostate are embraced by the fibres of the levator ani muscle, which 

 practically blend with the compressor urethrse muscle and surround the membranous 

 urethra. The muscular fibres passing from the longitudinal layer of the rectum to the 

 membranous urethra have been called by Proust the recto-urethralis muscle ; they 



