306 ANIMAL PHYSIOLOGY. 
of duodenal flexure ; 10, second branch of same; 11, origin of floating portion of small 
intestine ; 12, small intestine ; 12’, terminal portion of this intestine, flanked on each side 
by the two ceca (regarded as the analogue of colon of mammals) ; 13, 13, free extremities 
of ezecums ; 14, insertion of these two culs-de-sac_ into intestinal tube ; 15, rectum ; 16, 
cloaca ; 17, anus ; 18, mesentery ; 19, left lobe of liver ; 20, right lobe ; 21, gall-bladder 
22, insertion of pancreatic and biliary ducts ; the two pancreatic ducts are the most ante- 
rior, the choledic or hepatic is in the middle, and the cystic duct is posterior ; 23. pancreas; 
24, diaphragmatic aspect of lung ; 25, ovary (in a state of atrophy) ; 26, oviduct. 
Man’s teeth are somewhat intermediate in form between the 
carnivorous and the herbivorous type. Birds lack teeth, but 
the strong muscular gizzard suffices to grind the food against 
the small pebbles that are habitually swallowed. 
The crop, well developed in granivorous birds, is a dilata- 
tion of the esophagus, serving to store and soften the food. 
In the pigeon a glandular epithelium in the crop secretes a 
milky-looking substance, that is regurgitated into the mouth 
of the young one, which is inserted within that of the parent 
bird. ' 
The proventriculus—an enlargement just above the gizzard 
—is relatively to the latter very thin-walled, but provides the 
true gastric juices. , 
Certain plants digest proteid matter, like animals; thus the 
sun-dew (Drosera), by the closure of its leaves, captures insects, 
which are digested and the products absorbed. The digestive 
fluid consists of a pepsin-containing secretion, together with 
formic acid. 
THE DIGESTIVE JUICES. 
Saliva.—The saliva as found in the mouth is a mixture of 
the secretion of three pairs of glands, alkaline in reaction, of a 
specific gravity of 1002 to 1006, with a small percentage of 
solids (‘2'per cent), consisting of salts and organic bodies 
(mucin, proteids). , 
Saliva serves mechanical functions in articulation, in moist- 
ening the food, and dissolving out some of its salts. But its 
principal use in digestion is in reducing starchy matters to a 
soluble form, as sugar. So far as known, the other constituents 
of the food are not changed chemically in the mouth. 
The Amylolytie Action of Saliva.—Starch exists in grains, sur- 
rounded by a cellulose covering, which saliva does not digest; 
hence its action on raw starch is slow. 
It is found that if a specimen of boiled starch not too thick 
be exposed to a small quantity of saliva at the temperature of 
the body or thereabout (37° to 40° C.), it will speedily undergo 
certain changes: 
1. After a very short time sugar may be detected by Feb- 
