THE PERITONEUM, 



971 



or fj.eaov svrepois, middle intestine); that to the colon, the mesocolon ; that to the 

 sigmoid flexure, the mesosigmoidea or sigmoid mesocolon ; and that to the rectum, 

 the mesorectum. This has not been represented in the above figures for the sake 

 of simplicity. There is also a ventral mesentery, but not of such extent as the 

 dorsal. It extends along the front of the alimentary canal from the throat to 

 the lower end of the duodenum and in front as far down as the umbilicus 

 (Fig. 589). It almost makes the body-cavity a paired structure. In the upper 

 part of this mesentery is developed the heart, the part enclosing it being called 

 mesocardium anterius and posterius. The lower part extends from the stomach 

 and duodenum to the anterior wall and has many names ventral gastric and 

 duodenal mesentery, liver-ridge and prohepaticus ; it is never called anterior 

 mesogastrium. 



The liver is here developed anterior to the stomach, budding from the anterior 

 part of the beginning of the duodenum (Fig. 590). 



The pancreas buds from the posterior part of the duodenum, vertical at first 

 and covered on both sides by the mesentery of the small intestine ; it passes into 

 the mesogastrium later and becomes transverse. 



The spleen is developed in the second month in the mesogastrium and is not 

 connected directly with the alimentary canal. 



At this stage*, passing from before backward, we find the structures arranged : 

 anteriorly, liver; in the centre, stomach; posteriorly, spleen and pancreas. The 

 anterior mesentery in front of the liver becomes the suspensory or falciform liga- 

 ment of the liver, extending to the umbilicus below and embracing the intra- 

 abdominal part of the umbilical vein. The anterior mesentery between the liver 

 and stomach becomes the lesser amentum or lig. hepato-gastro-duodenale. The 

 mesogastrium between stomach and spleen becomes g astro-splenic omentum, and 

 that part between the spleen and vertebral column forms the great omentum. 



Fig. 591 is a cross-section of the same embryo. Anteriorly are the two sacs 

 of the liver projecting one into each side of the body-cavity. The right sac 

 grows to a larger size than the left; they form respectively the right and left lobes. 

 Behind these is the duodenum and behind that the pancreas. The intervening 



Posterior Wa, 

 Dorsal Mesentery 

 Pancreas 



Lig. Suspensorium 

 Hepatis 



FIG. 591. Cross section in duodenal 

 region to show same structures as in 

 Fig. 590. (Hertwig.) 



Stomach 



Geliacaxis 

 Mesogastrium 



Superior mes- 

 enteric artery 



Splenic flexure 



of colon 

 Inferior mes- 

 enteric artery 

 'Mesentery 



FIG. 592. Schematic representation of the mesentery in a six- 

 weeks' human embryo. (Toldt.) 



parts of the mesentery are called ligaments, viz. first, suspensory ligament of 

 liver, next Jtepato-duodenal ligament, next duodeno-pancreatic ligament, and lastly 

 the dorsal mesentery. Note that pancreas and duodenum are wholly enclosed. 



The vascular arrangement of this stage is shown in Fig. 592. The coeliac 

 axis, the superior mesenteric and inferior mesenteric arteries have their points of 

 supply definitely marked out even in the sixth week. They pass from the aorta 

 between the two layers of the mesogastrium and mesentery to their destinations, 

 which never change. The creliac axis goes to the stomach, spleen, pancreas, 

 liver and part of duodenum ; the superior mesenteric, to part of duodenum, the 



