30 
INTRODUCTION. 
twenty or more, but in by far the greater proportion of birds 
is twelve. 
Fig. 25. 
As great importance is justly attributed to the Digestive 
Organs, which vary much in form in the different tribes, 
and as I have always given the characters of those parts 
among those peculiarly distinctive of the orders, families, 
and genera, it is necessary here to say a few words respect- 
ing them. The gullet or oesophagus is that part which ex- 
tends in the form of a tube from the mouth to the stomach. 
It is often of nearly uniform width, but sometimes dilated 
into a crop. The stomach is a roundish or oblong sac, having 
three coats, the outer muscular, the next thin and dense, the 
inner usually membranous, dense, and rugous or wrinkled. 
The intestine is an elongated tube, wider in its first fold, 
which is named the duodenum, towards the end having two 
appendages, named cceca, sometimes very small, sometimes 
