THE ALIMENTARY TRACT 203 
trointestinal tracts. Classifications based upon habits of 
life (Raptores, Cantores, Natores), prove likewise too 
broad or too heterogeneous, while systems making 
character of food the chief criterion though apparently 
correct in reasoning and helpful in certain orders, 
(Accipitres, Gralli) are found to present copious excep- 
tions ; moreover we are imperfectly informed of the exact 
diet that many families require or resort to in absence of 
their preferred food. I shall therefore discuss the chief 
diseases and distributions according to our classification, 
preceding the discussion by a brief resume of the ana- 
tomical peculiarities of the avian alimentary tube. 
The first digestive burden falls upon the proventricle 
where the principal juices are secreted while the muscu- 
lar stomach or gizzard assumes the duty of gastric 
mastication. The lateral muscular bellies of its heavy 
wall grind the food and lYiix well the gastric juices. Its 
mucosa probably supplies only lubricant. In birds whose 
food is hard, corn and the like, this grinder is supplied 
with a dry horny internal layer, while a thick, moist, soft, 
epithelial surface is sufficient for carnivorous birds. All 
kinds of gradations exist between these extremes. The 
mucosa of the proventricle is always soft, but quite deep 
to permit the placement of compound tubular glands. 
The relation of size of these two parts is subject to 
many variations. (1) The proventricle is larger propor- 
tionately in meat eating, fish eating and fruit eating 
birds, the gizzard having the greater size in granivora 
and insectivora. In certain birds the mucosa of the two 
is separated by a very soft thin zone, an important fact in 
Psittaci since at this place spiroptera seem to penetrate 
to the glandular layer of both organs. 
The duodenum begins in practically all birds, from a 
spherical cavity at the pyloric end of the gizzard, to be 
accredited anatomically to both sections. It passes down- 
(1) See IVIagnan, Compt. Rendus d. I' Acad, de Science, 1910 and 1911, 
Vol. 150, 151, 152. 
