666 BIRDS. 
except that “a dental ridge” (see Mammals) has been 
detected in some embryos. A narrow tongue lies in the 
floor of the mouth; it is unimportant in the pigeon, but 
is often useful, as in parrots, woodpeckers, and hummihg- 
birds. Associated with the tongue there are numerous 
glands. On the roof of the mouth lie the posterior nares, 
and behind them the single aperture of the Eustachian 
tubes. The gullet expands into a thin-walled, bilobed, 
non-glandular crop, in which the hurriedly swallowed 
seeds are stored and softened. Especially at the breed- 
ing season, the cells lining the crop degenerate, and 
form “pigeon’s milk,” which both sexes give to the 
young birds. 
From the crop the food canal is continued into the 
glandular part of the stomach (the proventriculus), where 
gastric juice is secreted from large glands. 
Beneath the proventriculus is the gizzard, in which.the 
food is ground. The walls are very muscular, the fibres 
radiating from two tendinous discs; the internal surface is 
lined by a hard, horny epithelium; and within the cavity 
are small stones which the bird has swallowed. In hawks 
and fish-eating birds the gizzard region is, naturally enough, 
soft. The pyloric opening, from the gizzard into the 
duodenum, is very near the cardiac opening from the 
proventriculus into the gizzard. 
In the fold of the long duodenum lies the pancreas with 
three ducts, whose number points to the triple origin of 
the pancreatic rudiment in the embryo. Into the same 
region open two bile-ducts from the two-lobed liver, which 
is without a gall-bladder in the common pigeon, though 
this is present in some birds, and even in some species of 
pigeon. 
The small intestine is long; the large ‘intestine very short,—not 
more than a rectum two inches in length: At the junction of the 
small and the large intestine there are two short cca. In some birds, 
‘e.g. the fowl, these are of considerable length; in the ostrich they are 
very long ; there are three in many ducks and birds of prey ; there is 
only one in some fish-eating birds; in hornbills, parakeets, etc., they 
are absent. 
The cloaca has three divisions (see Fig. 369),—an upper part into 
which the rectum opens, a median patt into which the ureters and the 
genital ducts open, and a posterior region (proctodzeum), opening into 
