THE PERITONEUM. 321 



trabeculse of connective tissue. From these spring the capillary 

 veins, which unite and finally form the splenic vein, which is like- 

 wise very large, and leaves the organ at the hilus. Some of the 

 small arteries terminate in lacunce, or intercellular spaces of the 

 pulp, whence veins arise. ' Embedded in the spleen pulp are 

 numei'ous white bodies, the splenic vesicles, or Malpighian cor- 

 puscles, which are attached to the smaller arteries. They consist 

 of a retiform lymphoid tissue, in the meshes of which are colourless 

 lymph cells and capillary vessels, the tissue itself being continuous 

 with the retiform tissue of the pulp. The nerves come from the 

 solar plexus. 



The spleen is regarded by some as an internal refuge for blood 

 when cold is applied to the superficies of the body. Its use is 

 very obscure ; some maintain that it forms blood -corpuscles ; 

 Kolliker, that it is the agent of their destruction. The usual view 

 now taken is that the white blood-corpuscles are formed in it, 

 while the red corpuscles are broken up. It appears not irrational 

 to suppose that, becoming distended with blood during digestion, 

 one of its uses may be to raise the temperature of the food in the 

 stomach to the degree required. 



THE PERITONEUM. 



The abdomen and part of the pelvis are lined by the peri- 

 toneum. Like all serous membranes, it is comjDosed of a p)arietal 

 and visceral portion, which together form a complete sac, with 

 the organs it covers situated on its outer side. The internal 

 surface is smooth, free, moist, and covered by scaly epithelium ; 

 it secretes a serous lubricating fluid. The external or attached 

 surface adheres to the inner parietes of the abdomen and pelvis, 

 excepting the centre of the diaphragm, and also to the outer 

 surfaces of the viscera, the former constituting the parietal, the 

 latter the thinner visceral portion. Besides covering the external 

 surface, of the viscera, double folds pass from one organ to another, 

 or from an organ to the parietes of the cavity; these double 

 folds of peritoneum are known either as ligaments, mesenteries, 

 or omenta. In ligaments the two folds are strengthened by an 

 interposed layer of fibro-elastic tissue. A mesentery is a broad, 

 double fold of peritoneum, attached to the abdominal parietes 

 above, and containing a portion of the intestine in its free or 

 remote extremity. Between its folds we find blood-vessels, 



Y 



