432 ' THE HORSE. 
THE MUCOUS MEMBRANE OF THE PYLORIC SAC OF 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 fluid, which 
contains besides other matters, of which the acid, so variable in its nature, 
is the most remarkable, a peculiar organic compound known as pepsine, 
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 for the general purposes of 
that fluid. 
THE INTESTINES. 
THE INTESTINES, large and small, constitute a hollow tube, very vari- 
able 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 
though nature has only divided them into two portions, the small and 
large, yet anatomists have subdivided each of these into three more— 
namely, duodenum, jejunum, and ileum: ccecum, colon, and rectum. All 
have three coats: the external, or peritoneal, which is very partial in the 
duodenum and rectum; the middle, or muscular; and the internal, or 
mucous ; but the last two are also differently arranged in the large and 
small intestines. 
THE SMALL INTESTINES are about seventy feet long, and vary from an 
inch to an inch and a half in diameter, except at their commencement, 
where there is a considerable dilatation, forming a sort of ventriculus or 
lesser stomach. They are gathered up into folds, in consequence of the 
mesentery, which attaches them to the superior walls of the abdomen, 
being of very limited extent as compared with their length ; and thus they 
may be described as presenting two curves, a lesser mesenteric curvature, 
and an outer or free one covered by the peritoneum. ‘The outer layer 
of the muscular coat consists only of a few scattered fibres, while the 
inner one is circular in its arrangement, and though thin as compared 
with the stomach, yet it is easily distinguished. The mucous coat is 
gathered into a few longitudinal folds when empty, which are very 
marked at its commencement ; but there are no valvular appendages, as 
in the human intestines. It is everywhere studded with vl: or little 
projections, like the pile of velvet, through the open mouths of which the 
chyle is taken up; and beneath it are numerous glands, named after their 
discoverers. The small intestines are liberally supplied with blood by the 
anterior mesenteric artery. Commencing at the pyloric opening of the 
stomach, the small intestine swells out into a second little bag, having, 
like that organ, a large and small curvature, the former being presented 
to the lesser curvature of the stomach. The enlargement son ceases, 
and this part ofthe intestine (in England called duodenum) is bound 
up against the walls of the abdomen by the root of the mesentery and 
mesocolon. It then crosses the spine and enters the left lumbar region, 
where it becomes loose or floating in the cavity of the abdomen, being only 
retained by the mesentery (see plan, Fig. 2, page 426). About twenty 
