344 



THE ANATOMY OF THE HORSE. 



The Splenic Artery, a division of the cceliac 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 remarkable in having the outer coat formed of lymphoid tissue. 

 Here and there, in most mammals, this lmyphoid tissue forms distinct 

 swellings developed either uniformly around the arteries, or more 



or 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 macro- 

 scopic 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 support- 

 ing network of retiform connective- 

 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. 



Fig. 48. 



Cut Surface of Horse's Spleen 

 (semi-diagrammatic) showing 

 trabecular framework. 



STRUCTURE OF THE PANCREAS. 



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

 composed 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 OF THE KIDNEY. 



The kidney is invested by a fibrous capsule. In health this can 

 without difficulty be stripped off the kidney substance, to which it 



