The =small intestine= (Intestinum tenue) is the tube which connects the
stomach with the large intestine. It begins at the pylorus and
terminates at the lesser curvature of the cæcum. Its average length is
about seventy feet (ca. 22 meters). When distended its diameter varies
from two to four inches (5 to 10 cm.). Its capacity is about twelve
gallons (40 to 50 liters).
It is clearly divisible into a =fixed= and a =mesenteric= or floating
portion. The fixed portion is termed the duodenum, while the mesenteric
portion (Intestinum tenue mesenteriale) is arbitrarily divided into
parts termed the jejunum and ileum.[92]
The =duodenum= is about three to four feet (ca. 1 to 1.25 m.) long. Its
shape is somewhat like a horseshoe, the convexity being directed toward
the right. The =first part= is directed to the right and forms an
ᔕ-shaped curve. The convexity of the first part of the curve is dorsal,
of the second ventral. It lies on the middle and right lobes of the
liver, and presents two dilatations (Ampullæ) with a constriction
between them. The duodenal angle or head of the pancreas lies in the
concavity of the second curve, and here, five to six inches (ca. 12 to
15 cm.) from the pylorus, the pancreatic duct and the bile-duct pierce
the bowel wall. The =second part= passes upward and backward on the
right lobe of the liver and, on reaching the right kidney and the base
of the cæcum, it curves toward the median plane, opposite the last rib.
The =third part= passes almost transversely from right to left behind
the base of the cæcum, crosses the median plane under the third and
fourth lumbar vertebræ, and turns forward to become continuous with the
jejunum under the left kidney. The sacculations of the first part have a
diameter of three to four inches (ca. 7.5 to 10 cm.).
It is attached by a short peritoneal fold termed the =mesoduodenum=.
This fixes the first part of the duodenum closely to the liver and the
right dorsal part of the colon; the remainder is somewhat less closely
attached by it to the cæcum and right kidney, the sublumbar muscles, and
(more closely) to the terminal part of the great colon and the first
part of the small colon.[93]
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