898 THE ORGANS OF DIGESTION. 



peritoneum is not a closed sac, since the free extremities of the Fallopian tubes 

 open directly into the peritoneal cavity. The former constitutes the parietal, 

 the latter the visceral part of the peritoneum. The/ree surface of the membrane 

 is smooth, covered by a layer of flattened endothelium, and lubricated by a small 

 quantity of serous fluid. Hence the viscera can glide freely against the wall of the 

 cavity or upon one another with the least possible amount of friction. Its attached 

 surface is rough, being connected to the viscera and inner surface of the parietes 

 by means of areolar tissue termed the subserous areolar tissue. The parietal por- 

 tion is loosely connected with the fascia lining the abdomen and pelvis, but more 

 closely to the under surface of the Diaphragm and also in the middle line of the 

 abdomen. 



The peritoneum differs from the other serous membranes of the body in 

 presenting a much more complex arrangement an arrangement which can only 

 be clearly understood by following the changes which take place in the alimentary 

 canal during its development ; and therefore the student is advised to preface his 

 study of the peritoneum by reviewing the chapter dealing with this subject in the 

 section on Embryology. 



To trace the continuity of the membrane from one viscus to another, and from 

 the viscera to the parietes, it is necessary to follow its reflections in the vertical 

 and horizontal directions, and in doing so it matters little where a start is made. 



If the stomach is drawn downward, a fold of peritoneum will be seen stretching 

 from its lesser curvature to the transverse fissure of the liver (Fig. 488). This is 

 the g astro-hepatic or small amentum, and consists of two layers ; these, on being 

 traced downward, split to envelop the stomach, covering respectively its anterior 

 and posterior surfaces. At the greater curvature of the stomach they again come 

 into contact and are continued downward in front of the transverse colon, forming 

 the anterior two layers of the great or gastro-colic omentum. Reaching the free 

 edge of this fold they are reflected upward as its two posterior layers, and thus the 

 great omentum consists of four layers of peritoneum. Followed upward the two 

 posterior layers separate so as to enclose the transverse colon, above which they 

 once more come into contact and pass backward to the abdominal wall as the trans- 

 verse mesocolon. Reaching the abdominal wall about the level of the transverse 

 part of the duodenum, the two layers of the transverse mesocolon become separated 

 from each other and take different directions ; the upper or anterior layer ascends 

 (ascending layer of transverse mesocolon) in front of the pancreas, and its further 

 course will be followed presently. The lower or posterior layer is carried down- 

 ward, as the anterior layer of the mesentery, by the superior mesenteric vessels to 

 the small intestine, around which it may be followed and subsequently traced 

 upward as the posterior layer of the mesentery to the abdominal wall. From the 

 posterior abdominal Avail it sweeps downward over the aorta into the pelvis, where 

 it invests the first part of the rectum and attaches it to the front of the sacrum by 

 a fold termed the mesorectum. Leaving first the sides and then the front of the 

 second part of the rectum it is reflected on to the back of the bladder, and, after 

 covering the posterior and upper aspects of this viscus, is carried by the urachus 

 and obliterated hypogastric arteries on to the posterior surface of the anterior 

 abdominal wall. Between the rectum and bladder it forms a pouch, the recto- 

 vesical pouch, bounded on each side by a crescentic or semilunar fold ; the bottom 

 of this pouch is about on a level with the middle of the vesiculae seminales i. ?., 

 three inches or so from the orifice of the anus. When the bladder is distended the 

 peritoneum is carried up with the expanded viscus, so that a considerable part of 

 the anterior surface of the latter lies directly against the abdominal wall without 

 the intervention of the peritoneal membrane. 



In the female the peritoneum is reflected from the rectum on to the upper part 

 of the posterior vaginal wall, forming the recto-vaginal pouch or pouch of Douglas. 

 It is then carried over the posterior aspect and fundus of the uterus on to its 

 anterior surface, which it covers as far as the junction of the body and cervix 

 uteri, forming here a second but shallower depression, the utero-vesical pouch. It 



