316 THE ANATOMY OF THE HORSE. 



hand, communicate with the internal pudic vein. After receiving blood 

 from the walls of the rectum and small colon, the posterior mesenteric 

 veins forms by union with the splenic a very short trunk which joins 

 the anterior mesenteric to form the vena portse. 



Lymphatic Vessels of the Intestine. — In an ordinary dissecting-room 

 subject the lymphatic vessels will not be visible unless the animal is 

 emaciated and has been killed shortly after a meal, in which case the 

 mesenteric vessels may be seen without dissection. They will be recog- 

 nised as vessels with very thin walls and milky contents, coursing 

 between the layers of the mesentery, from the intestine towards the 

 anterior mesenteric artery. The lympathic vessels of the small intestine 

 are called lacteals. 



The Lymphatic Glands of the Intestine are very numerous. Those 

 of the small intestine are chiefly aggregated in the form of a cluster of 

 about thirty included between the layers of the mesentery, near the 

 anterior mesenteric artery; but a number are placed lower down in 

 the mesentery, along the course of the ileo-csecal artery. The glands 

 of the caecum are distributed in the form of two chains along the 

 track of the superior and inferior ceecal arteries, and numerous glands 

 are similarly placed on the colon along the course of the direct and 

 retrograde colic arteries. Those of the small colon and rectum are, 

 for the most part, placed on the wall of the bowel, at the edge of the 

 mesentery; but a few are included between the layers of the colic 

 mesentery. The lacteals from the small intestine and the lymphatic 

 vessels from the large intestine traverse these various groups of glands 

 on their course towards the receptaculum chyli. 



The Sympathetic Nerve. This nerve forms on the aorta, in front of 

 the anterior mesenteric artery, a great network termed the Solar plexus. 

 The solar plexus is at present concealed by the pancreas, but the student 

 has to notice the anterior and posterior mesenteric plexuses, which are 

 wholly or in part derived from it. 



The Anterior Mesenteric Plexus comprises numerous nerves already 

 met in dissecting the branches of the anterior mesenteric artery. The 

 nerves interlace around the arteries, and pass with them to gain the 

 bowel, where they farther interlace before penetrating its wall. 



The Posterior Mesenteric Plexus. — The branches of this plexus run in 

 company with the divisions of the artery of the same name. Its nerves 

 are derived in part from the aortic plexus, which is a backward con- 

 tinuation of the solar plexus, and in part from roots furnished by 

 the lumbar cord of the sympathetic. The ultimate branches are 

 distributed in the wall of the small colon and rectum. 



Directions. — The intestinal mass is now to be removed in the following 

 manner. The ropes must be unfastened from the left limbs of the 

 animal, while those on the right limbs are to be lengthened until the 



