THE STOMACH. 431 
rib it ascends towards the superior mediastinum, where it lies below and a 
little to the right of the posterior aorta. On reaching the crura of the 
diaphragm it passes through the opening made for it by the decussation of 
their fibres (see diaphragm), and is connected with the stomach about the 
centre of its anterior curve. Throughout this course it- has a muscular 
coat, composed of striped fibres at its commencement, but afterwards they 
are unstriped. It is lined by mucous membrane, which is very thick and 
white. 
THE STOMACH is situated on the left side of the abdominal cavity, im- 
mediately behind the diaphragm. It resembles in shape the bag of the 
Scotch bag-pipes, having two openings, two curvatures (a lesser and a 
greater), two surfaces, and two sacs, which are generally divided by a 
constriction as shown in the accompanying engraving. Its volume varies 
with its contents, but in the horse of average size it will not contain more 
than three gallons, while the stomach of man, whose weight is only one- 
eighth that of the horse, holds three quarts. It lies across the abdomen, 
with its anterior surface in contact with the diaphragm on the left side, 
and in the middle having the liver between it and the central tendon of 
that muscle. Its posterior face is in contact with the colon; its inferior 
or larger curvature with the spleen, attached to it by the omentum, and 
separated from the abdominal muscles by the curvatures which the colon 
here makes. The left, or cardiac sac, is in contact with the supero- 
lateral walls of the abdomen and the left extremity of the pancreas, 
approximating to the anterior border of the left kidney. The right, or 
pyloric sac, is in contact with the right lobe of the liver, and the curva- 
tures of the colon. Like the rest of the alimentary canal within the 
abdomen, 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 
cesophagus, 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 con- 
striction 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 con- 
stricted, and has several small folds of mucous membrane around it, which 
accounts for the absence of vomiting 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 
ordinary process of digestion. The muscular coat of the left sac is com- 
posed 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 through 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 porte ; and the nerves are derived from the pneumogastric 
and solar plexus of the sympathetic. 
