416 THE HUMAN BODY 



An interesting fact about the spleen is that no important 

 function, such as would be supposed to exist in so large and 

 conspicuous an organ, is known for it. The spleen can be 

 removed from the body, in most species of animals, without 

 any noticeable effect on the after life of the animal. 



The most noteworthy physiological peculiarity of the organ 

 is its regular variation in size. During the digestive periods 

 the spleen swells slowly, shrinking again after digestion comes 

 to an end. The coincidence of these movements with the 

 digestive periods has led some to believe that the organ has a 

 function in connection with the digestion of food. Its structure, 

 on the other hand, seems to point to a function in connection 

 with the blood possibly the production of leucocytes or the 

 destruction of red corpuscles. It is known that during embryonic 

 life the spleen is a seat of red-corpuscle production, but in the 

 adult this activity disappears. 



The Blood-Vessels of Alimentary Canal, Liver, Spleen, and Pan- 

 creas. The stomach, the intestines, the pancreas, and the spleen 

 are supplied with arterial blood from three great branches of the 

 aorta. The most anterior of these, the celiac axis, springs from 

 the aorta close beneath the diaphragm and divides into the hepatic 

 artery, splenic artery, and arteries for the stomach; some of these 

 divisions may be seen in Fig. 135. The pancreas is supplied 

 partly from the hepatic, partly from the splenic artery. The two 

 other branches (superior and inferior mesenteric artery) are given 

 off from the aorta lower down in the abdominal cavity; the former 

 (5, Fig. 135) supplies the small intestine and half of the large, the 

 latter the remainder of the large. The blood passing through all 

 these arteries becomes venous in the capillaries of the organs they 

 supply, and is gathered into corresponding veins (Fig. 135) which 

 unite near the liver to form the portal vein, which, as already 

 noted, differs from all other veins in that it receives blood from 

 one set of capillaries and delivers it to another set. The further 

 course of the blood carried to the liver (partly arterial from the 

 hepatic artery, partly venous from the portal system) has been 

 described already (p. 412). 



