THE NOSTRILS AND NASAL FOSSAE — -THE GAPE. 29 



perforate when there is no septum (partition) between them, so that you can 

 see througli them from one side of the bill to the other, as in the turkey- 

 buzzard, crane, etc. ; imperforate when partitioned off from each other, as 

 in most birds ; but different ornithologists use these terms interchangeably. 

 The principal shapes of the nostrils may be thus exhibited : — a line, linear 

 nostrils; a line variously enlarged at either end, clavate, club-sluqKd, ob- 

 long, ovate nostrils ; a line, enlarged in the middle, oval or elliptic, nostrils ; 

 this passing insensiblj^ into the circle, round or circular nostrils ; and the 

 various kinds of more or less linear nostrils may be either longitudinal, as 

 in most birds, or oblique, as in a few; almost never directly transverse 

 (up and down). Rounded nostrils may have a raised border or rim; when 

 this is prolonged they are called tubular, as in some of the goatsucker 

 family, and in all the petrels. Usually, the nostrils are formed entirely by 

 the substance surrounding them, thus, of cere, in a hawk, of softish skin, 

 in a pigeon, plover or snipe, or of horn, in most birds; but often their 

 contour is partly formed by a special development somewhat distinct either 

 in form or texture, and this is called the nasal scale. Generally, it forms 

 a sort of overhanging arch or portico, as well shown in all the gallinaceous 

 birds, among the wrens, etc. A very curious case of this is seen in the 

 European wryneck {lynx torquilla), where the scale forms the floor instead 

 of the roof of the nostrils. The nostrils also vary in being feathered or 

 nahed; the nasal fossa being a place where the frontal feathers are apt to 

 run out in points (called antioi) embracing the root of the culmen. This 

 extension may completely fill and hide the fossa, as in many grouse and 

 ptarmigan ; but it ofteuer runs for a varying distance toward, or above and 

 beyond the nostrils; sometimes, similar]}^ below them, as in a chimnej^- 

 swift ; and the nostrils may be densely feathered when there is no evident 

 fossa, as in an auk. When thus truly feathered in varjing degree, they are 

 still open to view ; another condition is, their being covered over and hidden 

 by modified feathers. These are usually bristle-like {setaceous), and form 

 two tufts, close-pressed, and directed forwards, as is perfectly shown in a 

 crow ; or the feathers may be less modified in texture, and form either two 

 tufts, one over each nostril, or a single ruff, embracing the whole base of the 

 upper mandible; as in nuthatches, titmice, redpoll linnets, snow buntino-s 

 and other northern Fringillidoi. Bristles or feathers thus growing forwards 

 are called retrorse (L. retrorsum, backward ; here used in the sense of in an 

 opposite direction from the lay of the general plumage ; but they should 

 properly be called antrorse, i. e., forward). The nostrils, whether culminal 

 or lateral, are, like the eyes and ears, always two in number, though they 

 may be united in one tube, as in the petrels. 



§ 53. The Gape. It only remains to consider what results from the re- 

 lations of the two mandibles to each other. When the bill is opened, there 

 is a cleft, or fissure between them ; this is the gapie or rictus (L. rictus, 

 mouth in the act of grinning) ; but, while thus real 13^ meaning the open 

 space between the mandibles, it is generally used to signify the line of their 



