4 ANIMAL FORMS 
juice. From the stomach it is made to enter the intestine, 
and is further acted upon by fluids from the liver, the 
Fig. 2.—Diagram of heart and blood- 
vessels of the squirrel or other 
mammal. 4@.o., aorta; h, vessels 
of head ; Z.a., left auricle ; J.ea., 
vessels of lower extremities ; lg., 
jung; 2.v., left ventricle; p.a., 
pulmonary artery ; 7.7., pulmo- 
nary vein; 7.a., right auricle; 
7.v., right ventricle ; v., vessels of 
viscera. Arteries are represented 
by heavy walls. 
pancreas, and the-glands of the 
intestines themselves. Thus 
treated it becomes changed from 
an insoluble state into a fluid 
which readily penetrates the 
coats of the digestive tract. 
Many of the organs of the 
body are placed at a considera- 
ble distance from the food as 
it comes through the coats of 
the stomach and intestine. In 
order to supply them with the 
necessary nourishment a distrib- 
uting apparatus is required. 
This is the office performed by 
the circulatory system, for as 
rapidly as the food penetrates 
the walls of the digestive tract 
it enters the blood, and by the 
beating of the heart is driven 
to all parts of the body, which 
are thus continually kept in a 
state of repair. The blood serves 
also to remove waste substances 
from the various structures or 
organs of the animal body and 
to transfer them to the kidneys, 
skin, or lungs, which effect their 
removal from the body. 
4, Muscular and nervous sys- 
tems.—Owing to the fact that 
animals, as a rule, are compelled 
to move about in search of food, we find two highly devel- 
oped systems, the muscular and nervous, which are absent 
