DISSECTION OF THE DOG 25 



The disposition of the peritoneum in connection with the hver cannot be 

 adequately studied at this stage of the dissection : it will be better, therefore, 

 to postpone its examination until the liver itself can be displayed completely. 



Recessus duodeno-jejtjnalis.— If the mass of small intestine be turned 

 over towards the right and an examination be made immediately caudal and to 

 the left of the root of the mesentery where the abrupt curve of the intestine 

 marks the junction of duodenum and jejunum, the opening of the small duodeno- 

 jejunal recess will be disclosed. The depth of the recess varies. It may extend 

 along the right side of the ascending part of the duodenum to the second 

 flexure of this tube. 



A. MESENTERiCA CRANiALis. — The cranial mesenteric artery should be 

 looked for at the root of the mesentery about the point at which the transverse 

 colon crosses the middle line. In exposing it, it will be necessary to remove 

 a large lymph-gland, the largest ui the body, which lies at the root of the 

 mesentery and is associated with the commencement of the portal vein. This 

 corresponds to the separate lymph-glands of the stomach, liver, and spleen, 

 and some mesenteric glands of other animals. The commencement of the 

 mesenteric artery has a mesenteric sympathetic ganglion (ganglion mesentericum 

 craniale) related to it. Nerves from the ganglion form the cranial mesenteric 

 plexus (plexus mesentericus cranialis) and accompany the branches of the 

 artery. 



The cranial mesenteric artery is a branch of the abdominal aorta. It soon 

 divides into (1) a main continuation from which arise the intestinal arteries, 

 and (2) the common trunk of the middle colic, right colic, and ileo-cmco-colic 

 arteries. 



Aa. intestinales. — About fifteen intestinal arteries arise at intervals 

 from the main continuation of the mesenteric artery and run down the mesentery 

 to the small intestine, but before reaching the alimentary tube each artery 

 divides and the adjacent branches anastomose. Thus a series of arterial 

 arches are produced. Along the side of the mesenteric artery opposite to that 

 from ^vhich the intestinal arteries arise, a small group of mesenteric lymph - 

 glands will be found. The first of the intestinal arteries supplies a considerable 

 amount of the duodenum and anastomoses with the duodenal branch of the 

 pancreatico-duodenal artery ; and the last artery similarly anastomoses with 

 the ihac branch of the ileo-cseco-coUc artery. 



A. COLICA MEDIA. — The middle colic artery leaves the common trunk early 

 and is the largest branch "of the trunk. It supplies the transverse colon and 

 a considerable stretch of the descending colon. 



A. COLICA DEXTKA. — The right colic artery, a comparatively small vessel, 

 suppUes the ascending colon. 



A. iLEO-c^co-COLiCA. — The ileo-cseco-colic artery divides into three 

 branches which supply the ileum, caecum, and the commencement of the 

 ascending colon. The iliac branch anastomoses with the last intestinal artery. 



