604 ABDOMEN 



which forms the anterior and greater part of the pelvic dia- 

 phragm. It has a triple origin. The anterior fibres arise from 

 the back of the pubic bone between the attachments of the 

 visceral and parietal layers of the endo-pelvic fascia; the 

 posterior fibres arise from the pelvic surface of the ischial 

 spine ; the intermediate fibres, constituting the greater part 

 of the muscle, take origin in the angle between the visceral 

 and parietal layers of the pelvic fascia. 



Insertion. The anterior fibres pass downwards and back- 

 wards. A few of them are inserted into the central point of 

 the perineum, others are inserted into the wall of the anal 

 canal, between the internal and external sphincters, and some 

 join with the intermediate fibres, which sweep round into the 

 angle between the posterior wall of the rectum and the upper 

 end of the anal canal, where they unite with their fellows of 

 the opposite side and form a strong muscular collar round 

 the gut ; the lower fibres of this group are inserted into the 

 posterior wall of the anal canal between the two sphincters. 

 The posterior fibres pass backwards and medially, and are 

 inserted into the median ano-coccygeal raphe behind the 

 rectum, and into the side of the lower part of the coccyx. 

 The anterior fibres of the muscles of the opposite sides 

 embrace the lateral surfaces of the prostate as they pass back- 

 wards, and are frequently called the levatores prostates. (Fig. 

 239). As the intermediate and posterior fibres pass to their 

 insertions they support the infero-lateral surfaces of the 

 bladder and the lateral walls of the rectum. When the 

 muscle contracts, as a whole, it tends to elevate the pelvic 

 viscera. The fibres inserted into the wall of the anal canal 

 will pull that wall upwards over descending faeces, and will 

 therefore aid defaecation. The fibres which form the collar- 

 like loop round the angle between the rectum and the anal 

 passage will, on contraction, increase that angle, and tend to 

 prevent the passage of the contents of the rectum into the 

 anal passage. 



M. Coccygeus. This is a small triangular muscle which 

 continues the plane of the pelvic diaphragm posterior to the 

 levator ani. It arises from the pelvic surface of the ischial 

 spine and the adjacent pelvic fascia, and, expanding as it 

 passes medially, it is inserted into the margin of the last piece 

 of the sacrum and the anterior surface of the upper part of the 

 coccyx. Its anterior margin is continuous with the levator ani, 



