CAVITY OF THE PELVIS. 



THE cavity of the pelvis is a part of the general abdominal space (p. 

 431), and is situate below the brim or inlet of the true pelvis. 



Boundaries. The space is surrounded by the firm bony ring of the 

 pelvic bones : it is bounded behind by the sacrum and the coccyx, with 

 the pyriformis muscles and the sacro-sciatic ligaments ; and laterally and 

 in front, by the innominate bones covered by the obturator muscles. 



Inferiorly, or towards the perinasum, the cavity is limited by the fascia 

 reflected from the wall to the viscera, and by the levatores ani and coccygei 

 muscles : only in this last direction, where the bounding structures are 

 movable, can alterations be made in the size of the space. 



Contents. In the pelvis are contained the urinary bladder, the lower 

 end of the large intestine or the rectum, and some of the generative or- 

 gans, according to the sex. All the viscera possess vessels, nerves, and 

 lymphatics ; and the serous membrane is reflected over them. 



SECTION I. 



PELVIC FASCIA AND MUSCLES OF THE OUTLET. 



ON the wall of the pelvis is a thin fascia (pelvic) which extends from 

 the brim to the outlet, and covers the obturator muscle. 



Dissection. To bring into view the pelvic fascia, the internal iliac ves- 

 sels, and the psoas (if this has not been removed in the dissection of the 

 lumbar plexus), are to be taken away on the left side of the body. The 

 obturator vessels and nerve are to be cut through on the same side ; and 

 the peritoneum being detached from the wall of the pelvis, the fascia will 

 be seen on scraping away with the handle of the scalpel a large quantity 

 of fat. By this proceeding the membrane is dissected in its upper half, 

 or as low as the situation of a piece of fascia (recto-vesical) which is at- 

 tached to the viscera. 



To display the lower half, the student must ra : se the outlet of the pelvis ; 

 and, should the perineum be undissected, the fat must be taken from the 

 ischio-rectal hollow. The lower part of the fascia will now appear on the 

 outer side of that fossa, as it covers the obturator muscle. 



An additional step for showing the arrangement of the fascia may be 

 taken, by removing the external obturator muscle and the obturator mem- 

 brane, and then scraping away through the thyroid hole the obturator in- 

 ternus muscle, so as to look at the fascia through that aperture. 



