POSTERIOR HALF OF THE SPACE. 387 



or prepared pelvis, on which the ligaments remain entire ; and the student 

 should trace on the body the individual boundaries with his finger. In 

 front is the arch of the pubes ; and at the posterior part is the tip of the 

 coccyx, with the great gluteal muscles. On each side in front is the por- 

 tion of the innominate bone which forms the pubic arch, viz., from the 

 pubes to the ischial tuberosity ; and still further back is the great sacro- 

 sciatic ligament extending from the tuber ischii to the tip of the coccyx. 

 This region sinks into the outlet of the pelvis as far as the recto-vesical 

 fascia, which forms its floor. 



Form and size. The interval included within the boundaries above said 

 has the form of a lozenge, and measures about four inches from before 

 backwards, and three inches between the ischial tuberosities. 



Depth. The depth of the perinaeum from the surface to the floor may 

 be said to be generally about three inches at the anus, but this measure- 

 ment varies in different bodies ; and it amounts to about an inch near the 

 pubes. 



Division. A line from the front of the tuberosity of one side to the 

 corresponding point on the other, will divide the perinatal space into two 

 triangular parts. The anterior half (urethral) contains the penis and the 

 urethra, with their muscles and vessels and nerves. The posterior half 

 (rectal) is occupied by the lower end of the large intestine, with its mus- 

 cles, etc. 



POSTERIOR HALF OF THE SPACE. 



This portion of the perinteal space contains the lower end of the rectum, 

 surrounded by its elevator muscle and the muscles acting on the anus. The 

 gut does not occupy however the whole of the interval between the pelvic 

 bones ; for .on each side is a space, the ischio-rectal fossa, in which is con- 

 tained much loose fat, with the vessels and nerves for the supply of the 

 end of the gut. 



Dissection (fig. 129). The skin is to be raised from this part of the 

 perinamm by the employment of the following cuts : One is to be made 

 across the perineum at the front of the anus, and is to be extended rather 

 beyond the ischial tuberosity on each side. A second is to be carried a 

 little behind the tip of the coccyx in the same direction, and for the same 

 distance. The two transverse cuts are to be connected by carrying the 

 knife along the middle and around the anus. The flaps of skin thus marked 

 out, are to be raised and thrown outwards from the middle line : in detach- 

 ing the skin from the margin of the anus, the superficial subcutaneous 

 sphincter muscles may be injured without care, for they are close to the 

 skin, without the intervention of fat. The dissector should trace the 

 sphincter back to the coccyx, and forwards for a short distance beneath 

 the skin ; and define a fleshy slip at each side in front and behind to the 

 subcutaneous fatty layer. 



The next step is to bring into view the ischio-rectal hollow between the 

 side of the rectum and the tuberosity of the hip bone. On the left side 

 the fat is to be cleaned out of it without reference to the vessels and 

 nerves, but on the opposite side a special dissection is to be made of them. 

 To take out the fat from the left fossa, begin at the outer margin of the 

 sphincter ani, and proceed forwards and backwards. In front the dissec- 

 tion should not extend farther than the anus, whilst behind it should lay 

 bare the margin of the glutens maximus. On the inner side of the hollow 

 the levator ani (sometimes very pale) is to be dissected. On the outer 



