104 GENERAL ORNITHOLOGY. 
only meet at the extreme tip, or in the Wholegggel: family, where there is hardly more. As 
the student must see, the length of the gonys is simply a matter of how extensive is the fusion’ 
of the rami, and that, similarly, their mode of fusion, as in a sharp ridge, a flat surface, a 
straight line, a curve, ete., results in corresponding modifications of its special shape. The 
imterramal space is complementary to length of gonys: sometimes it runs to the tip of the bill, 
as in a pelican, sometimes there is next to none, as in a puffin; while its width depends upon 
the degree of divergence, and the straightness or curvature, of the rami. The surface between 
the tomium and lower edge of rami and gonys together is the side of the under mandible 
(fig. 26, m). The most important feature of the 
Upper Mandible is the culmen (Lat. for top of anything ; fig. 26, b). The culmen is to 
the upper mandible what the ridge is to the roof of a house; it is the upper profile of the bill 
—the highest middle lengthwise line of the bill ; it begins where the feathers end on the fore- 
head, 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 #-shaped; or double-convex, as in the 
tufted puffin: but in the great majority of cases it is convex, with increasing convexity towards 
the tip. Sometimes it rises up into a thin elevated crest, as well shown in the genus Cro- 
tophaga, and in the puffins (ratercula), when the upper mandible is said to be keeled, and the 
culmen itself 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 con- 
vex and sloping sides of the upper mandible (fig. 26, a). Ina 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; 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 upper mandible is the maxillary tomium, as far backward as it is hard 
and horny. The most conspicuous feature of the upper mandible im most birds is the 
Nasal Fossa (Lat. fossa, a ditch), or nasal groove (fig. 26, ¢), in which the nostrils open. 
The upper prong of the intermaxillary bone is usually separated some ways from the two 
lateral prongs; 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 ; swlews or groove when long and narrow; the former is well illustrated in 
the gallinaceous birds; the latter in nearly all wading birds and many swimmers. When the 
intermaxillary prongs are soldered throughout, or are very short and close together, there is 
no (or no evident) nasal depression, the nostrils then opening flush with the level of the 
bill. The 
Nostrils (fig. 26, d), two in number, vary in position as follows :— they 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 are basal, when at the base of the upper mandible; swb-basal when near it (usual) ; 
median when at or near the middle of the upper mandible (frequent, as in cranes, geese, ete.) : 
terminal when beyond this (very rare; probably there are now vo birds with nostrils at the 
end of the bill, except the Apteryx). The nostrils are pervious, when open, as in nearly all 
