THE DIGESTIVE SYSTEM 57 
(Wharton’s) forwards to open on the fore-part of the floor of the 
cavity of the mouth, below the apex of the tongue. These are the 
most largely developed and constant of the salivary glands, being 
met with in various degrees of development in almost all animals 
of the class. Next in constancy are (3) “the sublingual,” closely 
associated with the last-named, at all events in the locality in which 
the secretion is poured out; and (4) the “zygomatic” (z.gl), found 
only in some animals in the cheek, just under cover of the anterior 
part of the zygomatic arch, its duct entering the buccal cavity near 
that of the parotid. 
The most obvious function common to the secretion of these 
various glands, and to that of the smaller ones placed in the mucous 
membrane of the lips, the cheeks, the tongue, the palate, and fauces, 
is the mechanical one of moistening and softening the food, to 
enable it the more readily to be tasted, masticated, and swallowed, 
though each kind of gland may contribute in different manner 
and different degree to perform this function. The saliva is, 
moreover, of the greatest importance in the first stage or introduc- 
tion to the digestive process, as it dissolves or makes a watery 
extract of all soluble substances in the food, and so prepares them 
to be further acted on by the more potent digestive fluids met with 
subsequently in their progress through the alimentary canal. In 
addition to these functions it seems now well established by experi- 
ment that saliva serves in Man and many animals to aid directly 
in the digestive process, particularly by its power of inducing the 
saccharine transformation of amylaceous substances. As a general 
rule, in mammals the parotid saliva is more watery in its 
composition, while that of the submavxillaries, and still more the 
sublingual, contains more solid elements and is more viscid ;—so 
much so that some anatomists consider the latter, together with the 
small racemose glands of the cheeks, lips, and tongue, as mucous 
glands, retaining the name of salivary only for the parotid. These 
peculiar properties are sometimes illustrated in a remarkable 
degree, as, for example, the great secretion of excessively viscid 
saliva which lubricates the tongue of the Anteaters and Armadillos, 
associated with enormously developed submaxillary glands ; while, 
on the other hand, the parotids are of great size in those animals 
which habitually masticate dry and fibrous food. 
Stomach.—After the preparation which the aliment has under- 
gone in the mouth,—the extent of which varies immensely in 
different forms, being reduced almost to nothing in such animals as 
the Seals and Cetaceans, which, to use the familiar expression, 
“bolt” their food entire, and most fully carried out in the Rumin- 
ants, which “chew the cud,”—it is swallowed, and carried along 
the cesophagus by the action of its muscular coats into the stomach. 
In the greater number of mammals this organ is a simple saccular 
