524 
free barbs, called plumules. 
ZOOLOGY. 
Over the tail-bone (coccyz) are 
usually sebaceous glands, which secrete an oil, used by the 
Fig. 457.—Brain of the Hen. A, from above, 
B, from below; a, olfactory bulbs ; 6, cere- 
bral hemispheres; c, optic lobes; @, cerebel- 
lum; @’, its lateral parts; ¢, medulla.—After 
Carus, from Gegenbaur. 
bird in oiling and dress- 
ing or “preening” its 
feathers. In some birds, 
especially in the males of 
the gallinaceous fowls, as 
the cock and turkey, the 
head and neck are orna- 
mented with naked folds 
of the skin called ‘‘ combs” 
and ‘‘ wattles.” 
The brain is much iarger 
than in the reptiles, the 
cerebral hemispheres being greatly increased in size, while 
the cerebellum is transversely furrowed, and is so large as to 
cover the whole of the me- 
dulla. The alimentary tract 
consists of an cesophagus as 
long as the neck; it dilates 
in the domestic fowl and other 
seed-eating birds, as well as 
in the raptorial birds, into a 
lateral sac called the crop (i2- 
gluvies). The stomach is di- 
vided into two parts, the first, 
the proventriculus, which is 
glandular, secreting a digest- 
ive fluid; and the second, 
which corresponds to the pylo- 
ric end of the stomach in the 
mammals, is round, with mus- 
cular walls, especially develop- 
ed in seed-eating birds, and 
called the “ gizzard.” In the 
fowl the gizzard is lined with 
a firm horny layer, by which 
Fig. 458,—Thymus (¢h) and thyroid (A 
glands of a young hawk, Buteo vulgaris 
a Europe; itv, trachea.—After Gegen- 
aur. 
the food is crushed and comminuted, thus taking the place 
of teeth. The intestine (including the large and small intes- 
