48 



INTRODUCTION. 



replaces them in due order. Domestic birds are not fur- 

 nislied with so large a portion of this fluid as those which 

 live, in the open air. The feathers of the former are pervious 

 to every shower, while Swans, Geese, Ducks, and all those 

 which live upon the water, have their feathers dressed with 

 the oil from the first day of leaving the shell : where this oil 

 abounds, it usually renders the bird rank, and sometimes 

 very unpalatable as food. 



Thomson, in his Spring, thus alludes to this oleous 

 unction : 



" Hush'd in short suspense, 

 - The plumy people streak their wings with oil, 

 To throw the lucid moisture trickling off, 

 And wait the approaching sign to strike at once 

 Into the general choir." 



These oleous glands become sometimes diseased and tu- 

 mefied; the complaint is commonly denominated the Pip. 

 Tt is generally remedied by a simple puncture, by which 

 the collected fluid may be discharged. 



The Bones of birds vary in many particulars from those 

 of the mammalia. The chief difference, however, is, 

 that of the Sternum or breast-bone, which covers not 

 only what is called, in the mammalia, the thoracic viscera, 

 but also a considerable portion of the rest of the intestines. 

 This bone, in all the birds which fly, is distinguished by a 

 long ridge or keel, to which muscles may be and are at- 

 tached, to facilitate their flight ; that this keel is for such 

 purpose there can be no doubt, as in birds which do not fly, 

 the Ostrich for instance, the keel in the sternum is altogether 

 wanting. The cervical vertebrae are also much more nu- 

 merous in birds than in the mammalia, arising, of course, 

 from their greater length of neck. And the rings in the 



