344 



THE ANATOMY OP THE HORSE. 



V 



'\^ 



The Splenic Artery, a division of the coeliac axis, is a very large 

 vessel. Its branches enter at the concave border of the spleen, and 

 carry with them sheaths derived from the fibrous tunic. These 



branches reduce themselves by division, 



'* and the smaller .branches are remark- 



able in having the outer coat formed of 



*"" lym^jhoid tissue. Here and there, in 



" s most mammals, this lymphoid tissue 



forms distinct svi'ellings developed either 



uniformly around the arteries, or more 



01 less to one side. These are the 



malpighian bodies of the spleen. The 



spleen of the horse, as a rule, does not 



contain malpighian bodies of macroscopic 



size. The arteries terminate in tufts 



of capillary vessels in the pulp. They 



are believed to have incomplete walls, 



allowing their contents to escape and 



form the pulp. The rootlets of the 



splenic vein begin in the same manner, 



having incomplete walls through which 



their lumen is continuous with the 



spaces lodging the pulp. Gradually 



their walls become thicker and complete, 



and adjacent veins uniting on their 



course towards the anterior border form the large splenic vein, which is 



one of the main branches of the portal vein. 



The Splenic Pulp possesses a supporting network of retiform con- 

 nective-tissue ; and the meshes of this network are set with many 

 lymphoid cells like the colourless corpuscles of the blood, and with red 

 blood corpuscles, normal or in different stages of disintegration. 



' B> 



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Fig. 48. 



Cut Surface of Horse's Spleen (semi- 

 diagrammatic), SHOWING TRABECU- 

 LAR FRAMEWORK. 



STRUCTURE OP THE PANCREAS. 



The pancreas is a compound tubular or racemose gland. It is com- 

 posed of lobules held together by a connective-tissue framework. When 

 the main ducts of the gland are traced backwards into the gland, they 

 are found to be formed by the union of smaller ducts, and so on until 

 the smallest ducts are reached. These begin in the alveoli, which are 

 lined by secretory epithelium. 



STRUCTURE OP THE KIDNEY. 



The kidney is invested by &. fibrous capsule. In health this can with- 

 out difficulty be stripped off the kidney substance, to which it is con- 



