PANCREAS — SPLEEN- OMENTUM. 231 



portion of the food from chyme into chyle, and separating it from that which, con- 

 taining little or no nutriment, is voided as excrement. 



Almost every part of it is closely invested by the peritoneum, which seems to dis- 

 charge the office of a capsule to this viscus. Its arteries are very small, considerintj 

 the bulk of the liver ; but their place is curiously supplied by a vein — the vena portcn 

 — a vessel formed by the union of the splenic and mesenteric veins, and which seems, 

 if it does not quite usurp the office and discharge the duty of the artery, to be far 

 more concerned than it in the secretion of the bile. There is a free intercouse between 

 the vessels of the two. 



There are, scattered through the substance of the liver, numerous little granules, 

 called acini, from their resemblance to the small stones of certain berries. They are 

 united together by a fine cellular web, whose intimate structure has never yet been 

 satisfactorily explained. From the blood which enters the liver there is a constant 

 secretion of a yellow bitter fluid, called bile. The separation of the bile from the 

 blood probably takes place within the acini ,- the secreting vessels are the penicelli, 

 or those which compose this fine cellular web, and the fluid — the bile — is taken up 

 by the pori hiliarii, small vessels, from which a yellowish fluid is seen exuding into 

 whatever part of the liver we cut, and is carried by them into the main vessel, the 

 hepatic duct. 



The bile, thus formed, is in most animals received into a reservoir, the gall-bladder, 

 whence it is conveyed into the duodenum (g, p. 221) at the times, and in the quan- 

 tities, which the purposes of digestion require; but the horse has no gall-bladder, 

 and, consequently, the bile flows into the intestine as rapidly as it is separated from 

 the blood. The reason of this is plain. A small stomach was given to the horse, in 

 order that the food might quickly pass out of it, and the diaphragm and the luncfs 

 might not be injuriously pressed upon, when we require his utmost speed, and also 

 that we might use him with little danger compared with that which would attach to 

 other animals, even when his stomach is distended with food. Then the stomach, so 

 small, and so speedily emptied, must be oftener replenished; the horse must hr 

 oftener eating, and food oftener or almost continuously passing out of his stomach. 

 How admirably does this comport with the uninterrupted supply of bile ! 



THE PANCREAS. 



In the domestic animals which are used for food, this organ is called the mveel-hread . 

 It lies between the stomach and left kidney. It much resembles in structure the sali- 

 vary glands in the neighbourhood of the mouth, and tlie fluid which it secretes has 

 been erroneously supposed to resemble the saliva in its properties. The pancreatic 

 fluid is carried into the intestines by a duct which enters at the same aperture with 

 that from the liver. It contains a large proportion of albumen, caseous matter, and a 

 little free acid. Its use, whether to dilute the bile or the chyme, or to assist in the 

 separation of the chyme from the feculent matter, has never been ascertained : it is, 

 however, clearly employed in aiding the process of digestion. 



THE SPLEEN. 



This organ, often called the melt, is a long, bluish-brown substance, broad and 

 thick at one end, and tapering at the other; lying along the left side of the stomach, 

 and between it and the short ribs. It is of a spongy nature, divided into numerous 

 little cells not unlike a honeycomb, and over which thousands of minute vessels 

 thickly spread. The particular use of this organ has never been clearly ascertained, 

 for in some cruel experiments it has been removed without apparent injury to diges- 

 tion or any other function. It is, however, useful, at least occasionally, or it woiili 

 not have been jjiven to the animal. It is perhaps a reservoir or receptacle for any 

 fluid that may be conveyed into the stomach beyond that which is sufficient for the 

 purposes of digestion. 



THE OMENTUM, 



Or cawl, is a doubling of the peritoneum, or rather consists of four layers of it. It 

 has been supposed to have been placed between the intestines and the walls of the 

 belly, in order to prevent concussion and injury during the rapid movement of the 

 animal. That, however, cannot be its principal use in the horse, from whom tho 

 most rapid movements are required ; for in him it is unusually short, extending only 



