328 THE ANATOMY OF THE HORSE. 



the posterior mesenteric plexus ; and an anterior mesenteric plexus, 

 already described. 



Directions. — The form, situation, and relations of the kidneys, and 

 the course of the ureters should now be examined. Without displacing 

 the kidneys, the fat and peritoneum is to be stripped from their lower 

 face, their vessels being carefully cleaned at the same time. The 

 ureter will be found passing backwards from the notched inner border 

 of each kidney, and it is to be followed backwards to the entrance 

 to the pelvis. In close relation to each kidney is its suprarenal body, 

 which, to prevent displacement, may be transfixed in position with 

 a long pin. 



The Kidneys (Plates 44 and 47) are the two glandular bodies that 

 secrete the urine. Each kidney occupies a position at the side of the 

 vertebral column, on the inferior aspect of the loins, and at the roof of the 

 abdominal cavity. In all except the most emaciated subjects, the kidneys 

 are surrounded by a quantity of adipose tissue, which is so abundant in 

 fat animals as to isolate them completely from surrounding objects. 

 The most common shape of the mammalian kidney is so well known 

 that it is popularly used as a descriptive term, objects having a similar 

 form being described as "kidney-shaped." Each kidney possesses two 

 surfaces, two borders, and two extremities. The inferior surface is 

 convex ; the superior, which is concealed at present, is almost flat. The 

 outer border is convex ; while the inner is concave, presenting a well- 

 marked notch termed the hilus. From this hilus the ureter issues, and 

 in its neighbourhood the renal vessels and nerves pass into or out of 

 the kidney. The extremities are anterior and posterior, and both are 

 rounded. It will at once be noticed, however (Plate 47), that although 

 this description applies to both kidneys, they are* far from being 

 identical in shape. The right kidney has an outline somewhat like the 

 "heart" of playing-cards, while the left has a decided resemblance to a 

 haricot bean. The right has the longest transverse, but the shortest 

 antero-posterior, diameter. The right is nearly symmetrical on each 

 side of a line drawn from the hilus to the middle of the outer border; 

 but if such a line be drawn on the left the part in front of the line 

 will be considerably smaller than the part behind it. 



Furthermore, it will be noticed that the two kidneys differ in 

 situation and in relations. The right kidney is the more anterior; 

 and, taking their relation to the skeleton, the difference may be 

 expressed thus: the right extends from the middle of the third last 

 intercostal space at its upper end to a point beneath the 2nd lumbar 

 transverse process ; the left extends from the second last intercostal 

 space to the 3rd lumbar transverse process. 



The right kidney is related by its upper face to the psoas muscles 

 and to the rim of the diaphragm ; by its lower face it contacts with 

 the pancreas and the crook of the caecum, and is partly covered by 



