314 THE STOMACH. 



iuconvenlence or danger, a smaller stomacli, in proportion to liis size, is 

 given to the horse than to almost any other animal. The bulk of the horse, 

 and the services required of him, demand much nutriment, and that of 

 such a nature as to occupy a very considerable space ; yet his stomach, 

 compared with his bulk, is not half so large as that of the human being : 

 therefore, although he, like every other animal, feels inconvenience from 

 great exertion immediately after a full meal, he suffers not so much as 

 other quadrupeds, for his stomach is small, and his food passes rapidly 

 through it, and descends to a part of the intestines distant from the dia- 

 phragm, and where the existence and pressure of the food cannot cause 

 him any annoyance. 



The stomach has four coats. The outermost is the lining of the cavity 

 of the belly, and the common covering of all the intestines — that by 

 which they are confined in their respective situations, and from which a 

 fluid is secreted that prevents all friction between them. This is a serous 

 membrane called the peritoneum — that which stretches round the outside 

 of the stomach. 



The second is the muscular coat, consisting of three layers of fibres, one 

 running lengthways, the other circularly, and the other obliquely, and by 

 means of wliich a constant gentle motion is communicated to the stomach, 

 mingling the food more intimately together, and preparing it for digestion, 

 and by the pressure of which the food when properly prepared is urged 

 on into the intestines. 



The third, or cuticular {shin-like) coat, c, covers a portion of the inside 

 of the stomach. It is a continuation of the lining of the gullet. _ There 

 are numerous glands on it, which secret a mucous fluid; and it is pro- 

 bably intended to be a reservoir in which a portion of the food is retained 

 for a while, and softened and better prepared for the action of the other 

 or true digestive portions of the stomach. The cuticular coat occupies 

 nearly one-half of the inside of the stomach. 



The other portion of the stomach is lined by the villous portion, from 

 which the true gastric juice is secreted, where the work of digestion 

 properly commences. The mouths of numerous little vessels open upon 

 it, poui-ing out a peculiar fluid, the gastric (stomach) juice, which mixes 

 with the food already softened, and converts it into a fluid called chyme. 

 As this is formed, it passes out of the other orifice of the stomach, the 

 'pylorus (doorkeepers),/, and enters the first small intestine; the harder 

 and undissolved parts being turned back to undergo farther action. 



Every portion of the muscular coat has the power of successively con- 

 tracting and relaxing, and thus, in the language of Dr. Bostock, 'the 

 successive contraction of each part of the stomach, by producing a series 

 of folds and wrinkles, serves to agitate the alimentary mass, and, by 

 brino-ing every part of it in its turn to the surface, to expose it to the 

 influence of the gastric juice, while at the same time the whole of the 

 contents are gradually propelled forwards, from the orifice which is con- 

 nected with the oesophagus to that by which they are discharged.' 



The pneumo-gastric nerve is the agent in producing these _ alternate 

 contractions and relaxations. It is the motor nerve belonging to these 

 parts. It has to keep the parietes of the stomach in contact with the 

 food, and the food in contact with the gastric juice. It has to bring the 

 difierent parts of the food in successive contact with the stomach, and to 

 propel them through this portion of the alimentary canal in order tha.t 

 they may be discharged into the duodenum. 



