346 



ABDOMEN 



-Fascia iliaca 

 -Peritoneum 



Bladder 



Sphincter Ani Externus. When this muscle is cleaned it 

 will be seen to consist of a thick ring of muscular fibres 

 surrounding the orifice of the anal canal. Posteriorly, it is 

 attached, by a pointed tendon, to the tip and posterior surface 

 of the terminal part of the coccyx ; anteriorly, it blends with 

 other perineal muscles in the central point of the perineum. 

 The fibres, in passing between these two points of attachment, 

 encircle the anal orifice and constitute a true sphincter 



muscle. Some of the 

 superficial fibres, both 

 in front and behind the 

 anal opening, are di- 

 rectly attached to the 

 skin. It draws its nerv- 

 ous supply from two 

 sources, viz., the fourth 

 sacral nerve and the in- 

 ferior hcemorrhoidal nerve. 

 Ischio-rectal Fossa. 

 Although the anal canal 

 is the largest and most 

 important object which 

 is contained within the 

 posterior portion of the 

 perineum, it does not fill 

 up the entire extent of 

 the anal triangle. An 

 interval or recess is left 

 upon each side of the 

 anal canal between it 

 and the ischium, and 

 to this recess is given the name of the ischio-rectal fossa. 



In shape the ischio-rectal fossa is pyramidal, the apex of 

 the pyramid being directed superiorly towards the pelvic 

 cavity, and the base inferiorly towards the integuments. The 

 medial wall of the space is sloping, whilst the lateral wall is 

 steep and perpendicular. 



Boundaries. Whilst the term " ischio-rectal" is applied to 

 this fossa, it must be borne in mind that neither the ischium 

 nor the anal canal enters directly into the formation of its walls. 

 Both are separated from the space by fascial and muscular 

 layers. Upon the medial aspect of the ischium is the obturator 



Obturator 

 internus 



Vesicula 

 seminalis 



Levator ani 



Pudendal 

 vessels 

 and nerve 

 Rectum 



FIG. 130. Diagram. The arrow is directed 

 upwards into the ischio-rectal fossa. The 

 parietal pelvic fascia is seen upon the 

 inner surface of the obturator internus. 

 Observe also the anal fascia clothing 

 the lateral surface of the levator ani and 

 the rectal fascia upon its medial surface. 



