Page:Laboratory Manual of the Anatomy of the Rat (Hunt 1924).djvu/96

82 Its attachment extends throughout nearly the whole ascending limb of the duodenum. Its connection with the descending colon is in common with that of the mesocolon.

The mesoduodenum spans the gap between the ascending and descending limbs of the duodenum. It joins the dorsal abdominal wall at the anterior end of the duodenal loop, as described below.

At its anterior end the duodenum turns sharply ventrad to join the jejunum. The mesentery of the jejunum and ileum serves also for the ascending colon, and is therefore both mesentery of the small intestine and a part of the mesocolon. The central axis of the mesentery carries the blood vessels which bear blood to and away from the intestines. The jejunum and ileum are very much longer than the axis of the mesentery. Therefore the mesentery's edge attached to them is expanded into many convolutions. This arrangement gives great freedom for movement of the small intestines, so that the peristaltic action, which forces the food along the canal, is not hindered by the mesenterial attachments. If an anaesthetized animal is opened, the movements of the small intestines can be seen.

The ascending colon is about as long as the axial portion of the mesentery. Therefore this edge of the mesocolon is not thrown into folds. A short triangular mesentery passes between the caecum and the distal end of the ileum. The transverse colon is tied to the mesoduodenum by a short mesentery. The length of the ascending mesocolon, as compared with the relatively short mesenterial connections of the transverse and descending colons, leaves the ascending colon relatively free for movement. Proximally this complex of jejunal and ilial mesenteries and mesocolon, fuses with the anterior part of the mesoduodenum. The combined mesenteries then join the dorsal wall of the ab