152 GENERAL ORNITHOLOGY part ii 



notice the special parts of either mandible ; and will begin with 

 the simplest, the 



Under Mandible. — In the majority of birds it is a little shorter 

 and a little narrower and not nearly so deep as the upper ; but 

 sometimes quite as large, or even larger. The upper edge, double 

 (i.e. there is an edge on both sides), is called the mandibular towmrn, 

 or in the plural, tomia (Gr. re/ivetv, temnein, to cut ; Fig. 26, j), as 

 far as it is hard ; this is received against, and usually a little within, 

 the corresponding edge of the upper mandible. The prongs already 

 mentioned are the mandibular rami (pi. of Lat. ramus, a branch ; 

 Fig. 26, i) ; these meet at some point in front, either at a short 

 angle (like >) or with a rounded joining (like ID). At their point of 

 union there is a prominence, more or less marked (Fig. 26, h); this 

 is the gomjs. That is to say, this point is gonys proper : but the 

 term is extended to apply to the whole line of union of the rami, 

 from gonys proper to the tip of the under mandible ; and in de- 

 scriptions it means, then, the under outline of the hill for a corre- 

 sponding distance (Fig. 26, I). This important term must be 

 understood ; it is constantly used in describing birds. The gonys 

 is to the under mandible what the keel is to a boat ; it is the 

 opposite of the ridge or culmen of the upper mandible. It varies 

 greatly in length. Ordinarily it forms, say, one-half to three- 

 fourths of the under outline. Sometimes, as in conirostral birds, 

 a sparrow, for example, it represents nearly all this outline ; while 

 in a few birds it makes the whole, and in some, as the puffin, is 

 actually longer than the lower mandible proper, because it extends 

 backwards in a point. Other birds may have almost no gonys at 

 all ; as a pelican, where the rami only meet at the extreme tip, or 

 in the whole duck 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, etc., results in corresponding modifications of its special 

 shape. The interramal 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 forehead, and extends to the tip of the upper mandible. 



