10 DISEASES OF DOMESTICATED BIRDS 
by the last three cervical and first thoracic spinal nerves in fowls, 
turkeys and pigeons. It furnishes branches to the pectoral region 
and wing. The pelvic region and legs are supplied by the lumbo- 
sacral plexus which is formed by two lumbar and four sacral spinal 
nerves. The spinal nerves vary in number according to the number 
of vertebrae present in each species. They arise from the spinal cord 
by two roots. The anterior or ventral root is motory, the posterior 
or dorsal, sensory in function. The ganglia on the latter are propor- 
tionately large. 
ALIMENTARY SYSTEM 
The alimentary system of birds differs to a considerable degree 
from that of other animals. There is no provision for mastication 
of food in the mouth owing to the absence of teeth. The food is 
taken up by the beak and is immediately passed by the tongue into 
the pharynx. From there it enters the esophagus and is carried to 
the crop where it is stored, partially softened, and slowly passed 
on to the proventriculus or glandular stomach. The gall bladder 
is absent in the pigeon and ostrich and occasionally in the guinea 
fowl. 
Mouth. The mouth is triangular in shape in such birds as the 
chicken, turkey, pigeon and canary. In the duck, goose and ostrich 
the mouth is comparatively long, with parallel borders and rounded 
anterior extremity. The roof of the mouth or hard palate is di- 
vided in the median line from near its anterior extremity to the 
pharynx, thus allowing free communication with the nasal passages. 
The soft palate observed in mammals is absent. The pharynx is 
relatively voluminous and permits the passage of large grains, or 
food masses. On its floor is the entrance to the larynx. The esoph- 
agus lacks the well developed muscular wall of mammals but rela- 
tively has a much greater diameter. 
Crop. Gallinaceous birds possess a crop or ingluvies which rep- 
resents a dilatation of the esophagus near its entrance to the thoracic 
cavity. Its wall, like that of the esophagus, consists of an outer 
membrane, a longitudinal muscular layer, a circular muscular layer, 
and an inner mucous membrane. Passage of its contents to the first 
stomach is aided by a wide circular muscle in the subcutaneous tissue 
surrounding the crop. Palmipeds, such as ducks and geese, are not 
provided with a distinct crop. Instead, the cervical portion of the 
esophagus may become greatly distended in such a manner as to form 
a long fusiform reservoir. 
