THE BXTBBlfAIi STEUCTTJEB OF BIEDS. 1 47 



nasal fossa ; if it is long and narrow it is called the nasal sulcus 

 or groove. They are usually lateral in position, but are called 

 culminal if they open on the culmen. When high, but not quite 

 80 high, they are superior, and they are inferior when nearer 

 the maxillary tomium than the culmen, and they may be quite 

 near the former — as in the Puffin. They are also usually basal 

 or subbasal (i. e. situated near the base of the bill), but some- 

 times they are median, as in the G-oose. In the Apteryx they 

 are terminal or at the end of the bill— a quite exceptional posi- 

 tion. "When the cere is feathered, they may be thus completely 

 hidden, and they may be also hidden by the extension forwards 

 of the frontal feathers of the head in pointed forward exten- 

 sions (called antice) on either side of the culmen — as in the 

 Grrouse. They may be also covered by setaceous feathers 

 which project forwards over them, and therefore project in 

 the contrary direction to that of the head-feathers generally, 

 or are what is termed antrorse in direction. Very rarely, 

 as in the Pelican, the nostrils do not open externally at 

 all, or are impervious. It may be that they can both be 

 seen through at the same time, or this may be impossible 

 owing to the existence of a median septum between them. 

 The terms perforate and imperforate are used to denote one or 

 other of these conditions. The shape of the openings may 

 vary from round to linear, and they are sometimes termed 

 oblong, ovate, oval, or elliptic, as may be deemed the most fit. 

 They are sometimes club-shaped or clavate. They may some- 

 times have a raised rim round them much prolonged — as in the 

 Petrels, and such are called tubular. Sometimes there is special 

 development called a nasal scale, which may overarch the 

 opening as in the Powl, or may form a partial floor as in the 

 Wryneck. The part of the biU between the nostrils is called 

 the mesorJiinum. 



The lower mandible is generally the smaller of the two, being 

 slightly surpassed by the upper at the tip and also laterally. 

 It is ' generally also less deep than the other. Its cutting-edge 

 is called the mandibular tomium, which bites against, and 

 generally a little within, the maxiUary tomium of the upper 

 mandible. Each half of the lower mandible is caUed a ramus, and 

 the two rami unite at the tip and for a greater or less distance, 

 thence backwards and downwards as the case may be. This 

 line of junction forms part of the lower margin of the lower 

 mandible, and corresponds with the culmen of the upper man- 

 . L 2 



