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 coeca, sometimes very small, sometimes 



