sis pubis above, to the point of
the coccyx below, is seen to traverse vertically the centres of the
urethra, the prostate, the base of the bladder, the anus, and the
rectum. These several parts are situated at different depths from the
perinaeal surface. The bulb of the urethra and the lower end of the
bowel are on the same plane comparatively superficial. The prostate lies
between these two parts, and on a plane deeper than they. The base of
the bladder is still more deeply situated than the prostate; and hence
it is that the end of the bowel is allowed to advance so near the
pendent bulb, that those parts are in a great measure concealed by
these. As the apex of the prostate lies an inch (more or less) deeper
than the bulb, so the direction of the membranous urethra, which
intervenes between the two, is according to the axis of the pelvic
outlet; the prostatic end of the membranous urethra being deeper than
the part near the bulb. The scalpel of the lithotomist, guided by the
staff in this part of the urethra, is made to enter the neck of the
bladder deeply in the same direction. On comparing the course of the
pudic arteries with the median line, A A, we find that they are removed
from it at a wider interval below than above; and also that where the
vessels first enter the perinaeal space, winding around the spines of
the ischia, they are much deeper in this situation (on a level with the
base of the bladder) than they are when arrived opposite the bulb of the
urethra. The transverse line B B, drawn in front of the anus from one
tuber ischii to the other, is seen to divide the perinaeum into the
anterior and posterior spaces, and to intersect at right angles the
median line A A. In the same way the line B B divides transversely both
pudic arteries, the front of the bowel, the base of the prostate, and
the sides of the neck of the bladder. Lateral lithotomy is performed in
reference to the line A A; the bilateral operation in regard to the line
B B. In order to avoid the bulb and rectum at the median line, and the
pudic artery at the outer side of the perinaeum, the lateral incisions
are made obliquely in the direction of the lines CD. In the bilateral
operation the incision necessary to avoid the bulb of the urethra in
front, the rectum behind, and the pudic arteries laterally, is required
to be made of a semicircular form, corresponding with the forepart of
the bowel; the cornua of the incision being directed behind.