EXTERNAL FARTS OF BIRDS. — THE BILL. 103 



sheath ijf either mandible may be pulled off whole, like the finger of a glove. It is, however 

 iu many bhds divided into parts, by various lines of slight couiiecticju, and then (-.(jmes off in 

 pieces; as is the case with some water birds, particularly ])etrels, where the divisions are regu- 

 lar, and the pieces have received distinctive names. Many auks {Alcida:) have the coverin" 

 of the bill in particular pieces, and it is an extraordinary fact that such parts are of a secondary 

 sexual character (see p. 90), being assumed at the breeding season and afterwards moidted 

 like feathers. Such condition (jf the sheath of the beak, or of special developments of the 

 slieath, is called cachtcous or deciduous. The entire covering of botli jaws together is called 

 rhuinpliot^ieca ((ir. paix(j>oi. liramplios, bealt ; BriKq, tjieke, a sheath), of the upper ainne, 

 rliiiiotheca (G-r. pis, liri.s, the nose) ; of the under, (jiuitliotheca (Gr. yva6oi, gnatlios, jaw) ; but 

 these terms are not mucli used, (c.) Tlie covering is otherwise variously marked ; sometimes 

 so strongly that similar features are impressed upon the bones themselves beneath. The most 

 frequent marks are various ridge.i (Lat. pi. caniue, keels) of all len.gths and degrees of expres- 

 sion, straight or curved, vertical, oblique, horizontal, lengthwise, or transverse ; a biU so 

 marked is said to be striate (Lat. stria, a streak) or carinate ; when numerous and irregular, 

 they are called ruga (Lat. ruga, a wrinkle) and the bill is said to be corrugated or rugose.^ 

 When the elevations are in p(]ints or spots instead of lines, they are called puncta (Lat. pmnc- 

 tum, a point) ; a bill so furnished is pitncta.te, but the last word is oftener employed to designate 

 the presence of little pnts or depressions, as in the dried bill of a snipe towards the end. Larger 

 softish, irregulai' knolis or elevations pass under the general name of !crtrfe or j;(:yj«7te, and a 

 bill so marked is papillose ; when the processes are very large and soft, the bill is said to be 

 carunculate (Lat. euro, flesh, diminutive caruncidus, little bit of flesh). Various linear deptres- 

 sions, often but not always associated with carinfe, are grooves or sulci (Lat. sulcus, a furrovv) 

 and the bill is then called sulcate. Sulci, like carinfe, are of all shapes, sizes, and positions ; 

 when very large and definite, they are sometimes called canalieuli, or channels. The various 

 knobs, "horns," and large special features of the bill cannot be here particularized. Any of 

 the foregoing features may occur on both mandibles, and they are exclusive of that special 

 mark of the upper the nasal fossa in which the nostrils open, and which is considered below. 

 We have still to 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 tomium, or iu the 

 plural, tomia (Gr. rijxveiv, 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 mentioneil are tlie mandibular rami (pi. of Lat. ramus, a branch ; fig. 26, *) ; 

 these meet at some point in front, eitlier at a short angle (like >) or with a rounded joining 

 (like !3). At tlieir point of union there is a prominence, more or less marked (fig. 26, k) ; 

 this is the GONi'S (corrupted from the Gr. yom, gonu, a knee; hence, any similar protuber- 

 ance). That is to say, this point is gonys proper ; but the term is extended to apply t(j the 

 whole line of imi(.)n of the rami, from gonys proper to the tip of the under mandible ; and in 

 descriptirjns it means, tlien, tlie under outline of tlie hill for a corresponding distance (fig. 26, J). 

 This important term must bo understood; it is constantly used in describing birds. Tlie 

 gonys is to the under mandilde 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 spiarrow foi 

 example, it represents nearly all this outline ; while in a few birds it makes the whole, and iu 

 some, as the puflin, is actually longer than the lower mandible proper, liecause it extends back- 

 wards in a point. Other birds may have abnost no gonys at all; as a pelican, where the rami 



