482 THE ANATOMY OF THE HORSE 



the abdomeu, the stomach is made up of three coats ; the external serous, 

 which is a continuation of the peritoneum ; the middle or muscular ; and 

 the internal, or mucous coat. On slitting it open and examining the 

 interior, it is at once apparent that the two sacs are very differently lined. 

 The cardiac mucous membrane resembles in appearance the interior of the 

 oesophagus, being whitish brown, tough, comparatively dry, and covered 

 with a thick layer of epithelium. On tracing the mucous membrane to the 

 left sac, it presents an abrupt line of demarcation opposite the constriction 

 between the two sacs. Beyond this, to the right, it is of a brownish red, 

 marbled with lighter shades of the same colour, easily torn, and covered 

 with a very thin epithelium. The left sac is in fact a simple reservoir of 

 food, while the right is the true organ of digestion. Each of the two 

 orifices also presents a peculiarity. The cardiac is slightly constricted, and 

 has several small folds of mucous membrane around it, which accounts for 

 the rarity of vomition in the horse. On the other hand the pyloric orifice 

 is larger, and is merely surrounded by a raised cushion, which no doubt 

 can be closed by the muscular sphincter, the fibres of which envelop it, 

 but which is most probably kept patent during the ordinaiy process of 

 digestion. The muscular coat of the left sac is composed of three planes, 

 the fibres of which pass in different directions, all tending to empty its 

 contents into the right. The latter sac is, however, surrounded by only 

 one plane of muscular fibres, all passing in a circular direction, forcing the 

 contents towards the pylorus. The arteries of the stomach are large and 

 numerous, being derived from the aorta thi-ough the superior gastric, the 

 right and left gastric, and the vasa brevia, which are given off by the 

 trunk of the splenic artery. The veins empty themselves into the vena 

 portfe ; and the nerves are derived from the pneumogastric and solar plexus 

 of the sympathetic. 



The mucous membrane op the pyloric sac op the stomach is made 

 up almost entirely of tubular follicles closely applied to each other, their 

 blind extremities resting upon the submucous cellular membrane, while 

 their mouths open into the stomach ; they are arranged in bundles or 

 groups, bound together by a fine areolar membrane, and the follicles from 

 each of these groups open into small pits or depressions, which may be 

 seen in the interior of this part. They secrete the gastric Jluid, which 

 contains besides other matters, of which the acid, so variable in its nature, 

 is [the most remarkable, a peculiar organic compound known as j)epsine, 

 which seems to be a main agent in the digestive process, acting, like 

 ptyaline, as a species of ferment, but of a more powerful kind. From the 

 researches of physiologists it appears that the acid is the solvent, while 

 the pepsine acts in converting the dissolved materials into a condition fit 

 for absorption into the blood, there to be used fur the general purposes of 

 that fluid. 



THE INTESTINES 



The intestines, large and small, constitute a hollow tube, very variable 

 in diameter, and measuring from eighty to ninety feet in length in an 

 average-sized horse. They extend from the stomach to, the anus: and 



