12 DISEASES OF DOMESTICATED BIRDS 
In pigeons the crop is divided into two lateral pouches. In both 
male and female, marked changes take place in the mucous mem 
brane shortly before the young are hatched. The membrane becomes 
thickened, epithelial cells are rapidly proliferated, undergo fatty 
degeneration and lead to the formation of a milky fluid which accu- 
mulates in the depressions between the ridges of the mucosa. This 
fluid is used to feed the young during the first days of life. 
A certain amount of fluid is secreted by the alveolar glands of the 
esophagus which together with the water consumed serves to soften 
grains to some extent and also to produce a slight fermentation of the 
crop contents. The crop has no secretory glands other than mucous 
glands. It is connected with the proventriculus or first stomach by 
a continuation of the esophagus which passes into the thoracic cavity 
and along the ventral face of the left lung. 
Proventriculus.. The proventriculus is small and fusiform in 
shape. Its walls are thick and contain numerous secretory glands 
which pour out gastric juice. The food is not held in the proven- 
triculus to be digested but after becoming saturated with the gastric 
secretion is forced into the gizzard where it is triturated by the 
powerful muscles of this organ with the aid of pebbles picked up 
by the bird. 
Gizzard. The gizzard or ventriculus bulbosus is a dense, mus- 
cular organ, flattened on two surfaces, with rounded border. In- 
ternally it is lined by a thick, tough, corrugated membrane which 
incloses a cavity of considerable volume, in which may be found 
food in various stages of disintegration and numerous pebbles, or 
bits of stone. Secretion of gastric juice also takes place in the 
gizzard according to Jobert. However, this organ acts principally 
in a mechanical way to grind the food and serves as a substitute 
for teeth. Its more highly developed in grain eating birds than 
in those subsisting principally on fish or animal food. In strictly 
carnivorous birds such as eagles, or hawks, the dense muscular wall 
is absent, or is limited to a portion of the organ, the remainder 
consisting of a membranous cul-de-sac. When reduced to a semi- 
fluid mass the food is released into the duodenum or first portion 
of the intestine, which joins the gizzard at a point near the entrance 
of the proventriculus. 
Intestines. On leaving the gizzard the duodenum extends pos- 
teriorly, bends on itself and returns to near its origin. Between 
its two parallel branches rests the pancreas which gives off its 
secretion into the lumen of the duodenum near its termination. 
