Jejunum.
—The jejunum is the second portion of the small intestines, it derives its name from the latin word “jejunas,” meaning empty, because it was formerly supposed to be empty after death.
It is wider, thicker, more vascular and of a deeper color than the ileum. The jejunum is about eight feet in length or two-fifths of the length of the small intestines.
The arteries which supply the jejunum are the branches of the superior mesenteric artery. The veins are of the same name.
The jejunum is fastened to the posterior wall of the abdomen by an extensive fold of the mesentery.
Ileum.
—The ileum is derived from a Greek word meaning to twist, and is so named on account of its numerous coils and convolutions. It is the third portion of the small intestines and is placed below the jejunum. It is much narrower and thinner than the jejunum, about twelve feet in length or three-fifths of the length of the small intestines. It is also attached to the posterior abdominal wall by means of the mesentery. The arteries which supply the ileum are the branches of the superior mesenteric artery. The veins are of the same name.
The villi are minute projections on the mucous membrane of the small intestines. They are largest and most numerous in the duodenum and jejunum, and become fewer and smaller in the ileum. It is in the villi of the intestines that we find the termination of the mesenteric arteries, the beginning of the mesenteric veins and the commencement of the lacteals.
As the food passes down the intestines, having been previously prepared in the stomach and intestines for absorption, it comes in very close contact with the villi of the intestines and it is here that the nutrition from the food is absorbed through the villi wall into the lacteals, and hence carried to the receptaculum chylii.