18 



EXTERNAL PARTS 



parrots the cere is generally covered witK feathers, and looks 

 much like a part of the forehead, but 'as the nostrils open 

 through it, it must be considered as part of the bill. 



Positions of the nostrils. — The nostrils are frequently in a sort 

 of hollow which has already been spoken of as a nasal fossa} 

 The groove, if long and narrow, is sometimes called the nasal 

 sulcus.^ Many birds show no evident fossae at all, but the 

 nostrils open flush with the surface of the bill.^ 



There are a number of terms used to denote the position 

 which the nostrils occupy in the upper mandible. They are 

 almost universally lateral,^ that is, on the sides of the mandi- 

 ble, away from the ridge ; rarely they are culmitial," that is, 

 together on the ridge of the culmen. The position on the 

 sides, with reference to the width and length of the man- 

 dible, is defined as follows : superior " indicates a position 

 above the central line between the culmen and the tomia, 

 and i»/f/'/or' below it; Sasa?* indicates a position at the fore- 

 head; sub-basal'^ neax it; median^" half way between the base 

 and the tip of the bill ; terminal " nearer the tip than- the 

 base. 



Kinds of nostrils. — The nostrils are usually open or pervious. 

 Sometimes they are not distinctly open, in which case they are 

 said to be impervious. Usually the two nostrils are sepa- 

 rated by a partition ; they are then said to be imperforate}^ 

 Earely it is possible to see through the nostrils from side to 

 side, as in the turkey buzzard, when they are said to be per- 

 forate.^^ 



Forms of nostrils. — A linear'^* nostril is elongated and of 



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