ALIMENTARY TRACT AND ITS APPENDAGES 313 
in front of and behind it (Fig. 150). No detailed account of its 
development exists. 
Stomach. It is well known that the stomach of birds exhibits 
two successive divisions, the proventriculus and the gizzard, 
the former of which has a digestive function and is richly pro- 
vided with glands, while the latter has a purely mechanical fune- 
tion, being provided with thick muscular walls, within which is 
the compressed cavity lined on each side by tendinous plates. 
On the third day of incubation, the divisions of the stomach 
are not recognizable, either by the form of the entire organ or by 
the structure of the walls. On the fifth day, however, the first 
indications of the formation of the compound glands of the 
proventriculus may be seen in the cardiac end; the posterior or 
pyloric end occupies the extreme left of the gastric curve and 
forms the rudiment of a blind pouch projecting posteriorly, that 
develops into the gizzard. On the sixth and seventh days this 
pouch expands farther in the same direction (ef. Fig. 179), and a 
constriction forms between the anterior portion of the stomach, 
or proventriculus, and the gizzard, as thus marked out. The 
gizzard grows out farther, to the left and posteriorly, at the same 
time undergoing a dorso-ventral flattening, owing to the forma- 
tion of the large muscle-masses. According to this account, 
therefore, the greater curvature of the gizzard would represent 
the original left side of the portion of the embryonic stomach 
from which it is derived, and the original right side would be 
represented by the lesser curvature. 
The large compound glands of the proventriculus are indi- 
cated on the fifth or sixth days as slight depressions of the ento- 
derm towards the mesenchyme; on the seventh day these become 
converted into saccular glands with narrow necks (Fig. 182). 
Each sacculus becomes multilobed about the twelfth or thirteenth 
days, and each lobulus includes a small number of culs-de-sac, 
lined with a simple epithelium. The last subsequently become 
tubular, and the original sacculus then represents the common 
duct of a large compound gland. (See Cazin.) 
The simple, tubular glands of the gizzard begin to form about 
the thirteenth or fourteenth day, and the lining of the gizzard 
is simply the hardened secretion of these glands; it is thus essen- 
tially different from cuticular and corneous structures of the sur- 
face of the body. According to Cazin, the glands of the gizzard 
