SPECIAL PARTS OF THE UNDER MANDIBLE. 27 
(L. caro, flesh, diminutive carunculus, little bit- of flesh). Various linear 
depressions, often but not always associated with carina, are grooves or sulct 
(L. sulcus, a furrow) and the bill is then swleate. Sulci, like carine, are of 
all shapes, sizes and positions; when very large and definite, they are some- 
times called canalicul7, or channels. The various knobs, “horns,” and large 
special features of the bill cannot be here particularized. Any of the fore- 
going features may occur on both mandibles, and they are exclusive of that 
special mark of the upper, in which the nostrils open, and which is consid- 
ered below (§ 51). We have still to notice the special parts of either 
mandible ; and will begin with the simplest, the 
§ 49. Unprr Manpisxe. 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 (7. e. there is an 
edge on both sides), is called the mandibular tomium (Gr. temnein, to cut ; 
fig. 5, 7), 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 (§ 44) are the mandibular rami (pl. of L. ramus, a branch; fig. 
5, 7); these meet at some point in front, cither at a short angle (like >) or 
with a rounded joining (like) ). At their point of union there is a promi- 
nence, more or less marked (fig. 5, /); this is the Gonys (corrupted from 
the Gr. gonu, a knee ; hence, any similar protuberance). 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 descriptions it means, then, the under outline of the bill for a corres- 
ponding distance (fig. 5, 7). This important term must be constantly held 
inmind. The gonys is to the under mandible what the keel is to a boat. 
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 puftin, is actually longer than the lower 
mandible proper, because it extends backwards in a point. Other birds 
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 the early or late 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 (§ 41, c) is complementary to length of gonys: some- 
times 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 diver- 
gence, and the straightness or curvature of the rami. The surface between 
the tomium and the lower edge of rami and gonys together is the s¢de of the 
under mandible (fig. 5, m). The most important feature of the 
§ 50. Urprr Manprsue is the culmen (Lat. for top of anything; fig. 5, 
6). The culmen is to the upper mandible what the ridge is to the roof of a 
