978 THE ORGANS OF DIGESTION. 



12. The mesentery of the colon transversum acquires a new line of attachment 

 running from right to left, and becomes differentiated from the mesentery as 

 mesoeolon. 



13. The mesogastrium of the stomach follows the torsions of the latter, and is 

 converted into the greater omentum, which grows out from the greater curvature 

 of the stomach to cover all the viscera lying below. 



14. Fusion of the walls of the omentum occur with the adjacent serous mem- 

 branes : (1) on the posterior wall of the body, where its line of origin from the 

 vertebral column is displaced to the left side of the body (Fig. 614) ; (2) with the 

 transverse colon and mesoeolon (Fig. 603) ; (3) anterior and posterior walls come 

 into close contact and fuse into an omental plate. 



Development of special organs out of the walls of the alimentary tube : 



1. From the intestinal canal proper there are formed only two glands, devel- 

 oped from the duodenum, viz. the liver and pancreas. 



2. The liver is developed as a branched tubular gland which becomes a net- 

 work : (a) There grow out from the duodenum into the ventral mesentery or pre- 

 hepaticus two liver-tubes, the fundaments of the right and left lobes of the liver. 

 (&) The tubes form hollow or solid branches, the hepatic cylinders, which become 

 in part bile-ducts and in part parenchyma of the liver. (<?) The common bile-duct 

 rises as an evagination of the wall of the duodenum receiving the two hepatic tubes, 

 and at one place an evagination which becomes the gall-bladder and cystic duct. 



3. From the ventral mesentery into which the liver grows are derived the sus- 

 pensory ligament of the liver (falciform) and the lesser omentum. 



4. The pancreas grows from the duodenum into the dorsal mesentery and into 

 the mesogastrium. 



The mesentery, which the pancreas originally possesses, disappears and fuses 

 with the posterior body-wall. By reason of the twist of the stomach, the long 

 vertical axis of the pancreas becomes transverse. 



ADULT PERITONEUM. 



During life and before dissection of the dead subject the abdominal cavity is 

 air-tight. Atmospheric pressure and muscular tension allow no space to be vacant. 

 The peritoneum (iteptrefvetv, to extend around) is the shiny serous membrane 

 lining the abdominal walls and posteriorly either lining the wall or covering the 

 viscera. If one is asked to touch the liver or stomach it is the peritoneum cover- 

 ing those organs which is touched. The peritoneal cavity was opened when the 

 anterior abdominal wall was incised, and does not exist till artificially produced 

 by the surgeon or dissector. 



In the male it is a closed sac with its two walls approximated, and consequently 

 perfectly empty except for a small amount of yellowish-green lubricating fluid, 

 liquor peritonei. Its anterior wall has already been opened and is called the 

 parietal peritoneum. Its posterior wall is tucked into every crevice and corner 

 around and between the viscera, which may be regarded as lying behind the whole 

 sac. This layer is largely visceral and the spaces between single organs are only 

 capillary. In the female, the peritoneum has two openings ; there is a single 

 region on either side where mucous membrane is continued into serous membrane, 

 viz. where the Fallopian tube opens into the peritoneal cavity. 



Other serous membranes are comparatively small, and, like the pleura, serous 

 pericardium, or tunica vaginalis, surround one organ. In these it is very easy to 

 trace the layer around the walls, then its reflection upon the viscus and off again 

 to the starting-point. In the peritoneum, or really behind it, we have many 

 organs involved, nearly all of which have experienced changes in size or position 

 during foetal life, so that the task is somewhat more complex. It is to trace the 

 peritoneal layers from one organ to another or from an organ to a wall, and to 

 show that the layers are continuous, making a closed sac. 



