754 



ORGANS OF DIGESTION. 



pleted, in well-fed animals, and especially in those fed upon albuminous diet. 

 In starved animals, they disappear altogether. 



The splenic artery is remarkable for its large size, in proportion to the size 

 of the organ; and also for its tortuous course. It divides into from four to six 

 branches, which enter the hilum of the organ, and ramify throughout its sub- 

 stance (Fig. 417), receiving sheaths from an involution of the external fibrous 

 tunic, the same sheaths also investing the nerves and veins. Each branch runs 

 in the transverse axis of the organ, from within outwards, diminishing in size 

 during its transit, and giving off, in its passage, smaller branches, some of which 

 pass to the anterior, others to the posterior part; these ultimately terminate in 

 the proper substance of the spleen, in small tufts or pencils of capillary vessels, 

 which lie in direct contact with the pulp. Each of the larger branches of the 

 arteries supplies chiefly that region of the organ in which the branch ramifies, 

 having no anastomosis with the majority of the other branches. 



Fig. 417. Transverse Section of the Human Spleen, showing the Distribution of the Splenic 

 Artery and its Branches. 



The capillaries, supported by the minute trabeculas, traverse the pulp in all 

 directions, and terminate either directly in the veins, or open into lacunar 

 spaces, from which the veins originate. 



The veins are of large size, as compared with the size of the organ ; and their 

 distribution is limited, like that of the arteries, to the supply of a particular 

 part of the gland; they are much larger and more numerous than the arteries. 

 They originate, 1st, as continuations of the capillaries of the arteries; 2d, by 

 intercellular spaces communicating with each other; 3d, by distinct caecal 

 pouches. By their junction they form from four to six branches, which emerge 

 from the hilum; and these uniting, form the splenic vein, the largest branch 

 of the vena portae. 



The lymphatics form a deep and superficial set; they pass through the lym- 

 phatic glands at the hilum, and terminate in the thoracic duct. 



The nerves are derived from branches of the right and left semilunar ganglia, 

 and right pneuinogastric nerve. 



