18 



EXTERNAL PARTS 



parrots the cere is generally covered with 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 f requentl)' 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 l)irds show no evident fossa? at all, but the 

 nostrils open flush with the surface of the bi)l.^ 



There are a number of terms used to denote the position 

 which the nostrils occupy in the upper nmndible. They are 

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

 ble, away from the ridge; rarely they are culmiual,^ 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 inferior^ below it; tasaZ" indicates a position at the fore- 

 head; siib-basaP UQAV it ; »«f'f/ /a // "^ half way between the base 

 and the tip of the bill; termhial^^ nearer the tip than the 

 base. 



Kinds of nostrils. — The nostrils are usually oj?e?j or jyorvious. 

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

 said to be im2)ervious. Usually the two nostrils are sepa- 

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

 Rarely 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 



