Digestive Organs of Birds. 127 
The nervous system of birds seems to me incapable of furnishing 
distinctive characters, because its parts are so similar in the different 
groups that, although they differ in each from any given standard, 
their differences cannot be intelligibly described. The same may 
be said of the vascular system, the respiratory, which, however, pre- 
sents many tangible differences, and the generative, which has re- 
ceived little comparative examination. The organs of sense afford 
many good characters, especially the tongue, which, however, is more 
to be considered as an organ of prehension than of gustation ; but 
they are too little diversified to form a basis of classification. The 
osseous and muscular systems, however, taken together, might afford 
a suitable basis ; but their characters would be more applicable were 
they taken in connection with the digestive, to which they might be 
viewed as subservient. An alimentary canal is common to all clas- 
ses of animals, and is in all more easily examined than any other ap- 
paratus, excepting the dermal ; and as the nature of the digestive 
organs determines the more characteristic habits and actions of birds 
and other animals, they are obviously entitled to the highest consi- 
deration. 
In Birds the digestive apparatus may, by superficial observers, be 
considered as very simple ; yet it is certainly as complex as in the 
Mammalia ; and as it presents modifications numerous and definable, 
easily observed and readily applied, it seems to me that, considered 
in all its parts, and taken as a centre of relations with respect to the 
other organs, it is better adapted for affording ordinal, family, and 
even generic characters, than any other. 
Were I therefore to propose a new arrangement of birds, I should 
base it on the digestive organs, or the intestinal canal, under which 
are to be included the bill, the tongue, the mouth, the pharynx, the 
oesophagus, the crop, the proventriculus, the stomach, the duode- 
num, the small intestine, the creca, the rectum, and the cloaca. The 
liver and pancreas, with the salivary glands, the mucous crypts, and 
the bursa Fabricii, might also be included. Some of these parts, as 
the bill and cloaca, are subservient to other purposes, but their pri- 
mary function has relation to digestion. 
I have been convinced by observation that correspondences in the 
part of this system of organs, are met by analogous correspondences 
in the habits and forms of birds ; and whether it should really be 
found entitled to form the basis of an arrangement or not, its exa- 
mination must tend to elucidate much that is obscure, and lead to 
important physiological results. 
The digestive organs of birds, considered in the different species. 
