28 SPECIAL PARTS OP THE UPPER MANDIBLE. 



house ; it is the upper profile of the liill — the highest middle lengthwise line 

 of the hill; it l)egiiis where the feathers end on the forehead, and extends 

 to the tip of the upper mandible. According to the shape of the bill it may 

 be straight or convex, or concave, or even somewhat c/j -shaped ; or double- 

 convex, as in the tufted puifin : but in the vast majority of cases it is con- 

 vex, with increasing convexity towards the tip. Sometimes it rises up into 

 a thin elevated crest, as well shown in Grotophaga (gen. 126) and in the 

 puffins, when the upper mandible is said to be heeled, and the culmen it- 

 self to be cultrate; sometimes it is really a furrow instead of a ridge, as 

 toward the end of a snipe's bill ; but generally it is simply the uppermost 

 line of union of the gently convex and sloping sides of the upper mandible 

 (fig. 5, a). In a great many birds, especially those with depressed bill, as 

 all the ducks, there is really no culmen; but then the median lengthwise line 

 of the surface of the upper mandible, takes the place and name of culmen. 

 The culmen generally stops short about opposite the proper base of the bill ; 

 then the feathers sweep across its end, and downwards across the base of the 

 sides of the upper mandible, usually also obliquely backwards. Variations 

 in both directions from this standard are frequent ; the feathers may run out 

 in a point on the culmen, shortening the latter, or the cUlmen may run 

 a way up the forehead parting the feathers ; thus either in a point, as in the 

 rails and gallinaceous birds, or as a broad plate of horn, as in the coots 

 and gallinules. The lower edge (double) of the u^oper mandible is the 

 maxillary tomium, as far backward as it is hard and horny. The most con- 

 spicuous feature of the upper mandible in most birds is the 



§ 51. Nasal Fossa (L. fossa, a ditch), or nasal groove (fig. 5, c), in 

 which the nostrils open. The upper prong of the intermaxillary bone ( § 44) 

 is usually separated some ways from the two lateral ones ; the skinny or 

 horny sheath that stretches betwixt them is usually sunken below the general 

 level of the bill, especially in those birds where the prongs are long or widely 

 separated ; this "ditch" is what we are about. It is called fossa when short 

 and wide, with varying depth ; sulcus or groove when long and narrow ; the 

 former is well illustrated in the gallinaceous birds ; the latter in nearly 

 all wading bii-ds and many swimmers. When the prongs are soldered 

 throughout, or are very short and close together, there is no (or no evident) 

 nasal depression, and the nostrils open flush with the level of the bill. The 



§ 52. Nostrils (fig. 5, d) vary in jiosition as follows : — thej^ are lateral 

 when on the sides of the upper mandible (almost always) ; culminal when 

 together on the ridge (rare) ; superior or inferior when evidently above or 

 below midway betwixt culmen and tomia ; they arc basal, when at the base 

 of the upper mandible ; sub-basal Avhen near it (usual) ; median when at or 

 near the middle of the upper mandible (frequent, as in cranes, geese, etc.) ; 

 terminal when beyond this (very rare ; and probably there are now no birds 

 with nostrils at the end of the bill, except the Apteryx). The nostrils are 

 'pervious, when open, as in nearly all birds; imjiervioxis, when not visibly 

 open, as among cormorants and other birds of the same order; they are 



