THE DIGESTIVE SYSTEM 81 



the Cyclostomes is more or less convoluted, and the parts 

 are held together by mesentery-like structures. The hepat- 

 ogastric ligament ties the stomach to the liver, the gas- 

 trosplenic ligament connects stomach and spleen, the hepat- 

 oduodenal ligament unites duodenum and liver. 



Though the mesenteries of the rat have doubtless evolved 

 from a simpler arrangement, such as that found in the 

 dogfish, they are relatively complex, and require careful 

 study. 



The mesogastrium of the rat is expanded into the form 

 of a sac, the greater omentum, which projects backward 

 from the stomach region. The rim of this sac unites with 

 the stomach upon a line extending from the pylorus along 

 the greater curvature of the stomach, around the left end 

 and back to the esophagus on the lesser curvature. Dorsad 

 the greater omentum unites with the body wall between 

 the adrenal glands. The omental sac thus comprises two 

 limbs, a dorsal one united anteriorly with the dorsal ab- 

 dominal wall, and a ventral limb attached to the greater 

 curvature of the stomach. 



The spleen is suspended along its median surface to the 

 left side of the omental sac. It lies parallel to the greater 

 curvature of the stomach. The part of the great omen- 

 tum connecting the spleen and stomach is the gastrosplenic 

 or gastrolienal ligament. A part of the pancreas is 

 lodged in the descending limb of the great omentum. 



The descending colon lies in the sagittal plane of the 

 body. It is held in this position throughout its length by 

 the relatively narrow mesocolon, which joins the dorsal 

 abdominal wall just beneath the inferior vena cava. The 

 mesocolon terminates about three' and one-half centimeters 

 from the anus. Anteriorly it fastens on the left to the 

 great omentum. The duodenocolic omentum connects the 

 descending colon and the ascending limb of the duodenum. 



