110 



ANATOMY AND PHYSIOLOGY OF 



arteries, and are equally distributed. The 

 posterior mesenteric vein is formed by sim- 

 ilar divisions to those coming oft' from the 

 posterior mesenteric artery, and then the 

 main trunk extends forwards and enters the 

 porta, near the termination of the splenic. 

 At this spot the veins from the small intes- 

 tine, as well as from the caecum and double 

 flexures of the colon, also contribute to 

 form the large portal trunk. 



The nerves of the intestines are derived 

 from the solar plexus, and they are found in 

 association with the arteries. The duo- 

 denum also receives branches from the par 

 vagum nerves, and the rectum and anus are 

 supplied also by divisions of the two last 

 sacral pairs. 



The lactal and lymphatic vessels of the 

 intestine are anatomically alike, and even 

 physiologically they admit of being com- 

 prehended under the same term, "lym- 

 phatic," because both absorb the fluid known 

 as lymph. But since the lymphatics of the 

 small intestine additionally contribute to 

 the function of chyliferous absorption, they 

 have been distinguished as lacteals, in con- 

 formity with the color of the fluid which 

 they take up during the digestive pro- 

 cess. 



The lacteals of the small, and lymphatics 

 of the large intestine, enter a set of lym- 

 phatic glands, by no means numerous, and 

 of small size, situated along the attached 

 border of the gut. From these the lacteals 

 ascend to about twenty-five or thirty lym- 

 phatic glands of larger size than the others, 

 situated at a short distance from the spine, 

 between the folds of the mesentery, from 

 which the lymph is then conducted into the 

 receptaculum chyli. From the large intes- 

 tine the lymphatics enter, in addition to the 

 intestinal set of glands, others situated in 

 the lumbar region, partly between the folds 

 of the meso-colon and meso-rectum, from 

 which the lymph is carried into the common 

 reservoir. 



The receptaculum chyli receives the fluid 

 from the lymphatic vessels of all the ab- 

 dominal viscera, as well as from other parts. 

 It is a membranous pouch of various 



calibre, lying in contact with the right crus 

 of the diaphragm, and right psoas muscle, 

 corresponding in situation to the second and 

 third lumbar vertebra;. It gradually con- 

 stricts anteriorly, and crossing the aorta to 

 get on its left side, enters the thorax, and 

 here becomes known as the thoracic duct, 

 which empties itself into the right axillary 

 vein. 



SPLEEN. 



The spleen, although, possibly, not bear- 

 ing any physiological connection with the 

 digestive process, still, from its anatomical 

 relations, conveniently admits of description 

 here. It is a singularly elastic organ, of a 

 purplish grey color; smooth on its outer 

 surface, and composed of a spongy texture, 

 enclosed in fi.brous tissue. The color of 

 the spleen is generally darker in herbivora 

 than in carnivorous quadrupeds, as in the 

 latter it is more of a red color. 



It is situated in the left hypochondrium, 

 and partly in the epigastrium, being at- 

 tached by its outer tunic to the stomach, 

 left kidney, and transverse colon. 



It is scythe-shaped, being small and 

 pointed anteriorly, but broad posteriorly. 

 It is smooth, and somewhat convex on its 

 inferior surface, whilst its superior one is 

 divided into two unequal halves, by a fissure 

 termed the hilum. The anterior division 

 is narrow, but the posterior one is broad 

 and triangular in shape. The margin of 

 the spleen is sharp all round. The size of 

 the organ varies considerably in different 

 subjects, and, according to circumstances, 

 in the same animal. 



The spleen is related, by its superior 

 surface, to the left end of the greater curva- 

 ture of the stomach, and to the diaphragm ; 

 at its broad base it is in close relation with 

 the left kidney ; its inferior surface is con- 

 nected with both double and single portions 

 of the colon. 



The spleen has two coats, a parenchyma, 

 blood vessels, nerves, and lymphatics, need- 

 ing separate description. 



The external coat is peritoneum, which 

 forms not only a covering to the organ itself, 



