284 THE HORSE. 



of vessels (vasa brevia), and also to effect some change in the blood 

 itself. 



THE PANCREAS. 



The pancreas is an elongated gland resembling in structure 

 the salivary glands, placed close to the spine, above the stomach. 

 It has two excretory ducts, which carry the pancreatic fluid se- 

 creted by it into the duodenum through a valvular opening com- 

 mon to it and the hepatic duct. The use of the pancreatic fluid 

 appears to be similar to that of the saliva. 



THE KIDNEYS. 



The kidneys are two oval organs situated beneath the psoas 

 muscles, and only retained in their position by the fatty cellular 

 membrane which envelops them, and by the upward pressure of 

 the other abdominal viscera below them. The right kidney is 

 completely within the ribs, but the left scarcely advances at all 

 beyond the eighteenth rib : each averages about forty ounces in 

 weight, but there is a considerable variation in size and form. 

 Unlike the corresponding organ in the cow, the horse's kidney is 

 not split up into lobules, though there is some little irregularity of 

 outline and surface. 



THE PELVIS. 



The cavity of the body known as the pelvis is situated be- 

 hind the abdomen, with which it communicates freely, each being 

 lined by a continuation of the peritoneum. A ridge of bone (the 

 brim of the pelvis) is the line of demarcation anteriorly. The 

 sacrum and os coccygis bound it superiorly, the anus posteriorly, 

 and the ossa innominata inferiorly and laterally. It contains the 

 bladder and rectum in both sexes, and in each the organs of gene- 

 ration peculiar to it. 



THE BLADDER. 



The bladder is a musculo-membranous bag destined to contain 

 the urine as it is gradually received from the ureters, which bring 

 it down from the kidneys. It lies in the middle of the pelvis, 

 occupying also more or less of the abdomen according to its con- 

 dition in point of repletion or emptiness. It is of an oval shape, 

 with its posterior extremity somewhat more pointed than the other, 

 and called its neck. At this point it gives origin to the urethra, 

 a canal for carrying off the urine. It receives the two ureters at 

 its superior surface, about an inch in front of the neck, where they 

 pierce the several coats in an oblique direction forming a complete 

 valve which prevents the return of the urine, and so invisible that 

 the presence of two openings is scarcely ever suspected by the 

 ordinary observer. Only about one-third of the bladder is covered 

 by the peritcr;eum the remainder being made up solely of the 



