Page 96 - Clinical Anatomy

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The gastrointestinal tract 81

quently completely obliterated in the elderly. Since obstruction of the
lumen is the usual precipitating cause of acute appendicitis it is not unnat-
ural, therefore, that appendicitis should be uncommon at the two extremes
of life.
2◊◊The appendicular artery represents the entire vascular supply of the
appendix. It runs first in the edge of the appendicular mesentery and then,
distally, along the wall of the appendix. Acute infection of the appendix
may result in thrombosis of this artery with rapid development of gangrene
and subsequent perforation. This is in contrast to acute cholecystitis, where
the rich collateral vascular supply from the liver bed ensures the rarity of
gangrene of the gall-bladder even if the cystic artery becomes thrombosed.
3◊◊Appendicectomy is usually performed through a muscle-splitting inci-
sion in the right iliac fossa (see ‘abdominal incisions’, page 62). The caecum
is delivered into the wound and, if the appendix is not immediately visible,
it is located by tracing the taeniae coli along the caecum— they fuse at the
base of the appendix. When the caecum is extraperitoneal it may be difficult
to bring the appendix up into the incision; this is facilitated by first mobiliz-
ing the caecum by incising the almost avascular peritoneum along its
lateral and inferior borders.
The appendix mesentery, containing the appendicular vessels, is firmly
tied and divided, the appendix base tied, the appendix removed and its
stump invaginated into the caecum.

The rectum
The rectum is 5in (12cm) in length. It commences anterior to the third
segment of the sacrum and ends at the level of the apex of the prostate or at
the lower quarter of the vagina, where it leads into the anal canal.
The rectum is straight in lower mammals (hence its name) but is curved
in man to fit into the sacral hollow. Moreover, it presents a series of three
lateral inflexions, capped by the valves of Houston, projecting left, right and
left from above downwards.

Relations (Figs 62, 63)

The main relations of the rectum are important. They must be visualized in
carrying out a rectal examination, they provide the key to the local spread
of rectal growths and they are important in operative removal of the
rectum.
Posteriorly lie sacrum and coccyx and the middle sacral artery, which
are separated from it by extraperitoneal connective tissue containing the
rectal vessels and lymphatics. The lower sacral nerves, emerging from the
anterior sacral foramina, may be involved by growth spreading posteriorly
from the rectum, resulting in severe sciatic pain.
Anteriorly, the upper two-thirds of the rectum are covered by peri-
toneum and relate to coils of small intestine which lie in the cul-de-sac of
the pouch of Douglas between the rectum and the bladder or the uterus.
In front of the lower one-third lie the prostate, bladder base and seminal