THE PERITONEUM. 



983 



So far we have seen the reflections and pouches in a longitudinal section in or 

 near the median line. 



It is the arrangement as found in the infant up to the age of two years ; after 

 that age the great omentum does not usually show a cavity. 



We should next trace the peritoneum transversely in cross sections. This is 

 simplest low doAvn in the abdomen, where only the greater sac is involved. Let 

 the section be made through the lumbar region somewhat above the level of the 

 umbilicus (Fig. 608). Beginning at the linea alba, trace the parietal layer 



Mesentery Aorta 



Small Lymphatic Vena cava, Ascending 

 intestine gland inferior colon 



Perito 



Left kidney 



FIG. 608. Peritoneal reflections in a transverse section of lumbar region below transverse colon. Seen 

 from above. Schematic. (From Tillaux.) 



around to the right until it nearly reaches the outer border of the Quadratus 

 lumborum muscle. It then passes up over part of the anterior surface of the 

 right kidney and meets the ascending colon. It partly surrounds it, forming 

 sometimes a proper mesocolon, but usually leaving one-third of the posterior sur- 

 face exposed. At birth only the anterior and external surfaces are covered. 



This layer then passes from the right kidney over the Psoas muscle, over the 

 vena cava. and. meeting the superior mesenteric vessels from the side, is led by 

 them to surround the small intestine, enclosing blood-vessels, lacteals, lymphatics, 

 and nerves in the mesentery proper. It next passes over the vertebral column and 

 aorta, anterior to the left Psoas muscle and left kidney, and covers the anterior 

 surface and sides of the descending colon, forming sometimes a true descending 

 mesocolon. It next is reflected upon the antero-lateral abdominal wall and is 

 continuous with itself at the linea alba. 



Notice that the lower end of each kidne^ mav be best felt by palpating to the 

 I-A * t. ii J * J r r 



right ot each colon. 



By taking a cross section higher up, just above the transverse colon, both 

 cavities are involved, making the tracing more complex, but the continuity of one 

 with the other is well seen. The spleen is met in this section, and all parts of 

 the colon are belonv (Fig. 609). Begin again in front at the linea alba and trace 

 to the right ; soon the layer makes a fold open to the front and encloses the 

 obliterated umbilical vein, now called the round ligament of the liver. The fold 

 is a part of the foetal anterior mesentery, now called falciform or suspensory liga- 

 ment of the liver. The layer is a parietal one, passes to the posterior abdominal 

 wall and covers the anterior surface of the right kidney and then passes in front 



