DIGESTION OF FOOD. 331 
epithelium, etc. These portions differ in digestive power, in 
the characteristics of the fluid secreted, and other details be- 
yond those which a superficial examination of this organ 
would lead one to suspect. 
The stomach of the horse represents a more advanced form 
of compound stomach than that of the hog, which is not evi- 
dent, however, until its glandular 
structure 1s examined closely. The 
entire left portion of the stomach 
represents an cesophageal dilata- 
tion lined with an epithelium that 
closely resembles that of the cesoph- 
agus, and with little if any digest- 
ive function. It thus appears that 
the stomach of the horse is in reali- 
ty smaller, as a true digestive gland, 
than it seems, so that a great part 
of the work of digestion must be 
done in the intestine ; though in Fie. 280.—Interior of horse's stomach 
this animal, if the food be retained —(fi¢r Chauveau). | 4. teft sac: B. 
long as it is in the hog, which is 
not, however, the general opinion as regards the stomach of the 
horse, salivary digestion may continue for a considerable period 
after the food has left the mouth. The secretion of mucus by 
the stomach in herbivora is abundant. 
THE MOVEMENTS OF THE DIGESTIVE ORGANS. 
As with other parts of the body, so in the alimentary tract, 
the slower kind of movement is carried out by plain muscu- 
lar fibers; and the movements, as a whole, belong to the class 
known as peristaltic; in fact, it is only at the beginning of the 
digestive tract that voluntary (striped) muscle is to be found 
and to a limited extent in the part next to this—i.e., in the 
cesophagus. 
Teeth in the highly organized mammal are remarkable in 
being to the least degree living structures of any in the entire 
animal, thus being in marked contrast to other organs. The 
enamel covering their exposed surfaces is the hardest of all the 
tissues and is necessarily of low vitality. We have already 
alluded to the difference in the teeth of different animals, and 
their relation to customary food and digestive functions. In 
fact, it is clear that the teeth and all the parts of the digestive 
