the rectosigmoid artery, is an area of potentially weak arterial anastomoses,
but that is further cranial. The superior mesenteric artery (answer a)dis-
tributes arteries to the small intestine right and middle colic arteries, that
supply blood as far distal as the splenic flexure of the transverse colon. The
left colic artery (answer b)anastomoses with the sigmoidal arteries. The
inferior mesenteric artery supplies the superior rectal artery, so answer cis
notcorrect. The principal branch of the external iliac artery is the femoral
artery (answer e).
388.The answer is a.(Moore and Dalley, p 322.)The descending colon is
controlled chiefly by parasympathetic innervation from the pelvic splanch-
nic nerves. Control of peristalsis is principally a function of the parasym-
pathetic division of the autonomic nervous system. Although removal of
the lumbar sympathetic chain (lumbar sympathectomy) does sever the
sympathetic fibers innervating the descending colon as well as the pelvic
viscera, [not thoracic splanchnics (answer c)] the action of sympathetic
fibers to the descending colon is mostly confined to vasoconstriction.
Because the parasympathetic innervation to the descending colon is
derived from the sacral outflow (S2–S4) through the pelvic splanchnic
nerves (nervi erigentes), [not by the vagus (answer b)] peristalsis will
occur normally after lumbar sympathectomy. Lumbar splanchnics do not
include L3 (answer d).Theanswer emakes no sense.
389.The answer is b.(Moore and Dalley, pp 202, 207.)The ilioinguinal
nerve innervates the portion of the internal oblique muscle inserting in the
lateral border of the conjoint tendon. Paralysis of these fibers would create
weakness in the conjoint tendon, allowing herniation to occur medial to the
inferior epigastric vessels. The genitofemoral nerve (answer a)supplies sen-
sory innervation to the skin of the femoral triangle and scrotum/labia
majora. The subcostal nerve (T12) (answer c)supplies lower portions of
the external abdominal oblique muscle. The pelvic splanchnic nerves
(answer d)supply autonomic (parasympathetic) innervation to the pelvic
viscera. The tenth thoracic spinal nerve (T10) (answer e)supplies abdom-
inal muscles superior to the inguinal region.
390.The answer is b.(Moore and Dalley, pp 270–271.)Meckel’s (ileal)
diverticuli are the most common congenital abnormality of the digestive
system. They are a remnant of the herniation and rotation of the midgut
Abdomen Answers 521