426 



BIRD. 



in the posterior part of the skull, is articulated behind 

 the centre of motion in the articulation of the jaw ; 

 and the one marked b, extends before it as far forward 

 as the gape ; but these are assisted by other muscles. 



Figure 2 is an outline of the tongue, which is as 

 curious as the other parts of this feeding apparatus. 



It will be seen that both mandibles have a double 

 curvature ; the upper one is curved downwards and 

 the lower one upwards, and the one curves to the 

 right and the other to the left, so that the points cross 

 each other ; and Mr. Yarrel found them to be about 

 three-eighths of an inch apart when the bill was 

 closed at the basal part. In the figure the upper 

 mandible curves to the right and the under one to the 

 left ; but that arrangement is reversed in many of 

 the specimens. The side to which the mandibles 

 turn is thus not a specific character of the bird. 



The upper mandible is united to the frontal bone 

 of the skull by plates of bone which are a little flexi- 

 ble, so that that mandible has a little lateral motion. 

 This agrees with that very general law in the animal 

 economy, in virtue of which every part which is 

 subject to violent motion or pressure is always so 

 formed as to give a little, by which means a sudden 

 strain upon the moving part is not so forcibly propa- 

 gated to the rest of the body ; but beyond this limited 

 motion, the base of the upper mandible is very 

 strongly supported. The lower jaw, the sides of 

 which are deep and strong, and the coronoid process 

 near the middle of their length, is so much elevated 

 as to give them all the stiffness of triangles, is articu- 

 lated by concave sockets upon spherical processes 

 on the os quadratum, and thus they admit of lateral 

 and oblique as well as vertical motion in that mandi- 

 ble. The pterygoid processes of the upper jaw are 

 very long, and the pterygoid muscles correspondingly 

 large ; and when the jaws are fully closed, that is, 

 when the coronoid process on each side is brought 

 into contact with the pterygoid on the same, the man- 

 dibles are cro*,>d to the full extent. The muscles 

 of that side of tu 'nead to which the lower mandible 

 curves, are larger than those of the other side, so that 

 their action has a tendency to draw the mandible 

 toward that side ; but as the closing muscles, which 

 have their insertion before the centre of motion, pull 

 the mandible to that side, the opening ones, which 

 are inserted behind that centre, pull it to the other ; 

 and thus the parts come in contact when the bill is 

 opened. The action of the bill thus resembles that 

 of a wedge, by the mandibles sliding upon each other, 

 and thrusting the points asunder at once with great 

 force and great firmness. 



Before stating how this bill is used, we mustadvert 

 to the tongue, which is an important part of the 

 whole organ. Fig. 2, on the cut is an outline of the 

 upper side. A portion of the tip from a to b is in the 

 form of a scoop, raised at the sides, and thin and 

 rounded at the extremity. This scoop is composed 

 of horn, supported by a particular bone, which is 

 articulated to the os hyoides or common bone of 

 the tongue c c, at the point b ; and one set of muscles 

 bind the joint at b, and thereby depress the point of 

 the scoop, and draw it backwards ; while another extend 

 the joint, and project and elevate the scoop. The 

 tongue has thus what may be called a sort of elbow 

 joint, and the scoop performs the office of a sort of 

 hand in picking up those substances to which access 

 is procured by the oblique motion of the mandibles. 

 The bill thus performs the functions of two bills ; 



and one of them could not performed by a bill of any 

 other construction. 



The way in which the points of the mandibles 

 move, draws them into any substance of which they 

 can take hold. If that substance is of a texture not 

 to be cut by the points, they split it open by their 

 wedge-like action; and if it is a softer substance, they 

 at the same time cut it in the cross direction. What- 

 ever may be the depth of the opening, the eye also 

 sees to the bottom of it, and the scoop of the tongue 

 can reach it. The upper mandible is the part of the 

 bill at rest, and therefore to whichever side it bends, 

 the head is bent to the other, and the eye on it com- 

 mands all the space, which the point of the under 

 mandible pushes open, from the contact to the greatest 

 extent in crossing. 



Crossbills are found chiefly in the extensive pine 

 forests of the northern latitudes, where they live upon 

 the seeds of those trees. These seeds are contained 

 under tough woody scales, which continue pretty 

 close for some time after the seeds are ripe ; and the 

 chief labour of the bird is to raise these scales by the 

 oblique motions of the bill, till the seeds can be 

 scooped out by means of the tongue ; and they do 

 this, or even split a piece of dry wood into strips, 

 with great rapidity. Sometimes, from causes not very 

 well understood, as they are not regular migrants, 

 they leave their native forests in considerable num- 

 bers, and do no small damage to orchards of apples 

 by splitting the pulp in pieces to get at the pips. 



The strong muscles on the sides of the head give 

 them something of the air of parrots; and though 

 they are not climbers as these are, they resemble the 

 parrot tribe a little in their plumage. One species 

 (Loxia pytiopsittacus) is popularly termed the parrot 

 crossbill. Indeed, though their habitations are in 

 the opposite extremes of climate, and the parrots get 

 at their food by climbing, and prepare it by cracking 

 the rind or shell with the mandibles, while the cross- 

 bills get at theirs by flight, and raise the scales with- 

 out separating the cone from the tree, yet the two 

 families have many points of resemblance. 



Insectivorous bills or Dentirostres. The insectivo- 

 rous birds, when properly restricted, consist of those 

 genera only which have the common normal feet 

 with three toes before and one behind, all articulated 

 on the' same level, and thus have their more peculiar 

 characters in the bills, or the bills and the wings. They 

 are inhabitants of woods, copses, and bushes, those 

 being the places where insects are most abundant, 

 though some of them inhabit the margins of waters, 

 and nestle in holes of rocks, or under stones. They 

 all take their food either standing on the ground or 

 perching on the sprays, or they dart upon it by short 

 jerks from the ground or the perch. Their bills are 

 accordingly all snapping bills, generally light in their 

 structure, naving the upper mandible rather longer 

 than the under one, and notched near the tip, but 

 not so sharp pointed or so firm in the tomia generally 

 as the bills of vegetable feeders. The point of the 

 bill is the prehensile part of it; and the culmen of' 

 the upper mandible is usually a little arched to sup- 

 port that part. In those genera which are charac- 

 terised by superior boldness the bill is compressed, 

 and the upper mandible hooked at the tip, while in 

 the feebler ones it is rather depressed, and the tip 

 straighter. 



The shrikes, a figure of the bill of one of which is 

 annexed, are the most daring birds of this division, 



