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Woodpecker (Chrysopterus viridis) of this country, but it is seen in the greater and lesser spotted species.

The tongue has also a peculiar formation; it is vermiform, or worm-like, barbed at its point like the head of an Indian spear, and is capable, by means of the curious construction of its muscles, of being thrown out to a great length. In order to convey some notion of the manner in which this is effected, we have copied the figure given in Dr. Roget's Bridgewater Treatise, with the accompanying description and explanation.

[graphic][subsumed]

The figure represents the head of the Woodpecker with the skin removed, and the parts dissected. The tongue, a, is supported on a slender os hyoides, or lingual bone, to the posterior end of which the extremities of two very long and narrow cartilaginous processes are articulated. The one on the right side is shown in the figure nearly in the whole extent of its course at b, c, d, e, and a small part of the left. cartilage is seen at f. The two cartilages form, at their

junction with the tongue, a very acute angle, slightly diverging as they proceed backwards, until bending downwards at b, they pass obliquely round the sides of the neck, connected by a membrane, g; then, being again inflected upwards, they converge towards the back of the head, where they meet, and, being enclosed in a common sheath, are conducted together along a groove, which extends forwards, along the middle. line of the cranium, d, till it arrives between the eyes. From this point the groove and the two cartilages it contains, which are now more closely conjoined, are deflected towards the right side, and terminate at the edge of the aperture of the right nostril, e, into which the united cartilages are finally inserted. In order that their course may be seen more distinctly, these cartilages are represented in the figure at c, drawn out of the groove provided to receive and protect them.* These cartilages are put in action by a long and slender muscle attached to the inner margin of each, and a counteraction is caused by another set of fibres passing in front of the anterior portion of the cartilages. The cartilages themselves are nearly as elastic as steel springs, and thus a considerable expense of muscular power is saved, and the bird is enabled to protrude and withdraw its lengthened tongue with great rapidity and but little effort.

In the cut, h is the salivary gland which secretes a glutinous fluid, with which the tongue is overspread, and by means of which, it is said, ants and similar small insects adhering to it are drawn into the bill; but whether this be so or not, there is another * Animal and Vegetable Physiology, Dr. Roget.

method by which the Woodpecker takes its prey. The tongue is terminated by a horny, thorn-like point, which, when the tongue is protruded, transfixes the insect, and the cartilaginous barbs with which it is armed prevent the insect from disengaging itself, let it struggle never so violently. The tongue is immediately withdrawn into the bill, and the insect is removed by means of a fringe of hairs pointed backwards and placed in the back of the palate, and surrounding a longitudinal groove. It is supposed that in detaching the transfixed insect the horny end of the tongue is pointed to the back of the throat, and then being brought forward into its usual position, the fringe detaches the prey from the barbs.*

The muscles which move the bill and head are capable of very powerful action, and by their means the bird is enabled speedily to punch a hole in the wood even of a living tree. The rapidity with which a Woodpecker pecks away at its work is almost incredible, the strokes cannot be counted, nor is it easy to detect the motion of the head and neck.

The main office for which the structure of a Woodpecker has to be adapted, says Mr. Mudie, is that of maintaining with the under part of the body a vertical position on the bark of a tree, in such a manner as to have the head, the neck, and the spine, as far as the lumbar vertebræ (which have a little more motion in this bird than in some others), perfectly free, so that the point of the bill may command the largest possible surface which is compatible with the length of the neck, or move with that force and velocity which are

* Bewick.

necessary for hewing holes in the wood with the greatest certainty and expedition. For this purpose the long sternum and coracoids, with the keel and furcal bone on the exterior side of them, form a flat arc with its chord; the former applied to the tree, so that the fixed point upon which the head and neck move in pecking may be brought nearer to the surface,

or moved farther from it, according as may be necessary. If this part (which may be called the base of the bird when in action) had been straight, there would have been more stability in one position, but it would have been only in one, and in that one only where the vertical line of the bark happened to be straight, which is not often the case in those gnarly and decaying trees which afford the fattest pastures for Woodpeckers. This, however, would have made the bird work at a disadvantage in excavating a hole to any considerable depth, because, if the position of the centre of action had been immovably adjusted to any one distance, the action of the bird would have been less effective at every other; but the arched form of the keel enables the bird to keep the centre of action always adjusted for the maximum effect, and that with so slight a motion of the steady or pectoral part of its body, that it can hardly be perceived.

A very little extension of the tarsal joints brings the centre of action more to the tree, and a very little bending of the same joints removes it farther away. Nor is this ready adaptation of the centre to the greatest effect of the stroke the only result of that action of the tarsal joints by which it is produced; for there is the same nice adjustment of the degree of hold taken on the bark to the varying stability of the position. When the centre of action is removed to the greatest distance, the centre of gravity is thrown furthest out, in proportion to the line of the axis, and therefore the weight tends more to pull the bird from the bark; but the very same action of the tarsal joints which produces this causes the claws to take a firmer hold of the bark, and also the stiff feathers of the tail to bear more against it as a support. So also, when the centre of action is brought nearer to the tree, and the hold by the foot not so much required, the same extension of the tarsal joint which brings the axis more parallel to the tree eases the clutch of the foot in exactly the same proportion.

Thus, by one of the most beautiful instances of the harmony of parts with each other, the Woodpecker is enabled to work with equal stability and effect, while the axis of the body is at all possible angles to the line of the tree, within the range that is necessary for its habit; and yet the different parts of this very curious and apparently complicated organization are so flexible to other purposes, that the Woodpecker can at once become a wing-bird or a ground-bird, when such a habit is necessary.*

Natural History of Birds.

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