308 



DISSECTION OF THE ABDOMEN. 



transverse 

 meso-colon 



its ascend- 

 ing layer ; 



descending 

 layer and 

 mesentery ; 



in pelvis ; 



along front 

 of abdomen 



Small and 

 large bags : 



behind. At the great curvature they meet again, and give rise to 

 the great omen turn or epiploon (g om). After descending to the 

 lower part of the abdomen, they bend backwards and ascend to the 

 transverse colon, which they enclose in the same way as the stomach ; 

 and they are then continued to the posterior abdominal wall, forming 

 the transverse meso-colon (me). (It should at once be pointed out, 

 lest the student be misled, that the layers of the great omentum in 

 front of the transverse colon are usually adherent to one another, 

 and not separated by intervals, as represented in fig. 114, for the 

 purpose of clearness.) Opposite the anterior border of the pancreas 

 these two layers, which have been followed over the transverse 

 colon, part company, the one passing upwards, and the other 

 downwards.* 



The ascending layer is continued upwards in front of the pancreas 

 and diaphragm, and is then reflected on to the posterior surface of the 

 liver, where it covers the part called the Spigelian lobe, and passes 

 into the hinder layer of the small omentum. This layer, however, 

 cannot be traced in the present stage of dissection. 



The descending layer immediately passes off along the superior 

 mesenteric vessels to the small intestine (jejunum and ileum), forming 

 the mesentery (in}. 



From the root of the mesentery, this layer descends over the lower 

 end of the aorta and the promontory of the sacrum to the pelvis, 

 where it partly invests the viscera of that cavity. Thus, it covers 

 the upper part of the rectum and is reflected forwards therefrom 

 to the bladder in the male, or the uterus in the female, forming 

 a pouch between the two ; and after covering the upper part of 

 the bladder, it passes off at the front and sides to the abdominal 

 wall, forming the fossae before noticed in the inguinal region 

 (p. 292). 



Lastly, having left the bladder, the membrane is continued 

 upwards, lining the anterior wall of the abdomen and the under- 

 surface of the diaphragm, nearly as far as the spine ; there it is 

 reflected over the upper surface of the liver, and then, turning 

 round the lower border to the under-surface, it joins the anterior 

 layer of the small omentum. 



In the foregoing account it will be seen that two vertical circles 

 have been traced, which surround distinct cavities in figure 114. 

 The portion of the membrane which forms the circle behind the 

 liver and stomach is known as the small sac of the peritoneum ; 

 while the part in front of those organs, which is much more extensive, 



* In the foetus at an early period the reflected portion of the great omentum 

 is continued up to the spine ; and while the ascending layer passes upwards 

 over the pancreas as explained in the text, the posterior or descending layer 

 surrounds the transverse colon before passing into the mesentery, thus forming 

 a transverse meso-colon distinct from the great omentum. The front of the 

 transverse meso-colon then becomes adherent to the opposed part of the 

 great omentum, so that the two are united in a single process, and the colon 

 appears to be enclosed between the omerital layers. Occasionally traces of 

 the foetal condition are met with in the adult. 



