486 THE ANATOMY OF THE HORSE 



THE SPLEEN 



The spleen can scarcely be considered as a gland, inasmuch as it has no 

 excretory duct, but it contains within its substance a number of little bodies, 

 called Malpighian corpuscles, which most pi'obably perform the same office 

 as the absorbent glands. Its weight as compared with the whole body is 

 about the same as in man, whose spleen weighs six ounces, while that of the 

 horse rarely exceeds three pounds. It is attaclied by the lesser omentum 

 (a fold of the peritoneum) to the stomach (see Fig. 77, page 481), and occupies 

 the left side of that organ. It is covered by a serous coat continuous with 

 the peritoneum, and its internal structure is spongy, and made up of cells 

 which contain a large quantity of blood. 



The function of the spleen is not positively ascertained, but it is believed 

 to perform the office of a reservoir for the blood required by the stomach, 

 with which it is closely connected by a set 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 secreted by it into the duodenum 

 through a valvular opening common to it and the hepatic duct. The use of 

 the pancreatic fluid aj)pears to be similar to that of the saliva. 



THE KIDNEYS 



The kidneys arc two oval organs situated beneath the psoas muscles, and 

 only retained in their position by the fatty cellular membrane which en- 

 velops them, and by the upwai'd pressure of the other abdominal viscera 

 below them. The right kidney is completely within the ribs, but the left 

 scarcely advances at all bej^ond 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, as may be seen in the annexed figure, which was taken from a 

 specimen somewhat remarkable in these respects. A transverse section 

 shows the internal structure, which is composed of a central cavity, the 

 pelvis, into which the urine flows, and from which it is carried to the bladder 

 by the ureter. In this pelvis several conical projections are visible, having 

 minute openings around their apices, which are the terminations of the 

 tubuli uriniferi composing the substance of the internal part of the oi'gan. 

 The external is the true secreting portion, and in this are contained a 

 multitude of minute red glol)ular bodies, composed of a flexus of capillary 

 vessels, and of a coil of tube in connection with the uriniferous tubuli, both 



