82 ANATOMY OF THE RAT 



Its attachment extends throughout nearly the whole as- 

 cending 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 as- 

 cending 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- 



