186 
TRITURATING ACTION OF GIZZARD. 
of fluid secreted by its walls, just as it is in the paunch of 
ruminant quadrupeds. This crop is of enormous size in some 
of the grcmivorous (grain-eating) birds, such as the Turkey. 
The second stomach (or ventriculus succenturiatus) is the one 
in which the gastric juice is secreted; but this is seldom 
large enough to retain the food, which passes-on through it 
to the gizzard , a hollow muscle, furnished with a hard tendi¬ 
nous lining. In the granivorous birds this is extremely 
strong and thick ; and pieces of gravel are swallowed by 
them, which, being worked-up with the food by the action of 
the gizzard, assist in its reduction. In the rapacious flesh- or 
fish-eating birds, however, no such assistance is required, the 
food being easy of solution; the walls of their gizzard are 
thin, possessing but few tendinous fibres; and the three 
cavities of the stomach are almost united into one. 
201. Various experiments have been made to test the 
mechanical powers of the gizzard of Birds. Balls of glass 
which they were made to swallow with their food, were soon 
ground to powder; and the points of needles and of lancets, 
fixed in a ball of lead, were blunted and broken-off by the 
power of the gizzard, whilst its own internal coat did not 
appear to be in the least injured. On the other hand it has 
been ascertained, that grain enclosed in metal balls which 
protected it from the mechanical action of the gizzard, but 
which were perforated so as to afford the gastric fluid free 
access to their contents, was not in the least digested ; so that 
the utility, and even the necessity of this operation, become 
evident. 
202. As there are few animals, save the Mammalia, that 
perform any proper mastication in their mouths, the grinding 
down of their food (where it is of such a nature as to require 
it) must be performed in the stomach; and accordingly we 
find many tribes, belonging to different divisions of the animal 
kingdom, in which a gizzard, or something analogous to it, 
exists. It is possessed by almost all Cephalopods , and by 
many of the Gasteropoda In the walls of the stomach of 
some of these last, there is a considerable amount of mineral 
matter deposited, intermixed with the hard tendinous fibres 
of which they chiefly consist. A powerful gizzard is also 
found in many Insects , but here it is placed above the diges¬ 
tive stomach (fig. 112, c). The accompanying figure exhibits 
