(2251). The most remarkable form of teeth, one indeed that is unique, is met with in the Whalebone Whale (Balaena mysticetus.) The teeth in this Cetacean, indeed, are not instruments of mastication, but form a very curious apparatus, adapted to strain the waves of the sea as through a sieve, and thus obtain from the ocean a sufficiency of food for the sustenance of its monstrous body.

Mouth of the Whalebone Whale.

Fig. 396. Mouth of the Whalebone Whale.

(2252). The whalebone (as it is improperly called) is attached to the gums of the upper jaw, being arranged in thin flat plates of some breadth, and varying in length according to the size of the Whale *. These plates are placed in several rows, similar to teeth in other animals; they stand parallel to each other, having one edge directed towards the circumference of the mouth. The outer row is composed of the longest plates, and these are in proportion to the varying distances between the two jaws, some being fourteen or fifteen feet long, and twelve or fifteen inches broad; but towards the anterior and posterior part of the mouth they are very short.

* J. Hunter, on the Structure and (Economy of Whales (Phil. Trans. 1787).

(2253). Inferiorly each plate of whalebone is terminated by a broad fringe of horny fibres resembling hair; and, seeing that in some whales there are about three hundred plates composing the outer row on each side of the mouth, the reader may form some idea of the extent of this enormous strainer, whereby the little Clio borealis, and other small Mollusca that swarm so abundantly in the Northern ocean, are caught by shoals preparatory to their being swallowed.

(2254). For what is known concerning the growth of whalebone, we are indebted to John Hunter; and as it would be difficult to curtail his clear and concise description of the process, it is here given in his own words *: -

(2255). "The formation of whalebone is extremely curious, being in one respect similar to that of hair, horns, spurs, etc.; but it has besides another mode of growth and decay, equally singular.

(2256). "These plates form upon a thin vascular substance, not immediately adhering to the jaw-bone, but having a more dense substance between, which is also vascular. This substance, which may be called the nidus of the whalebone, sends out thin, broad processes answering to each plate, on which the plate is formed, as the cock's spur or the bull's horn on the bony core, or a tooth on its pulp; so that each plate is necessarily hollow at its growing end, the first part of the growth taking place on the inside of this hollow.

(2257). "Besides this mode of growth, which is common to all such substances, it receives additional layers on the outside, formed from the above-mentioned vascular substance, extended along the surface of the jaw. This part also forms upon it a semi-horny substance between each plate, which is very white, rises with the whalebone, and becomes even with the outer edge of the jaw. This intermediate substance fills up the spaces between the plates as high as the jaw; acts as abutments to the whalebone; or is similar to the alveolar processes of the teeth, keeping them firm in their places.

(2258). "As both the whalebone and intermediate substance are constantly growing, and as we must suppose a determined length necessary, a regular mode of decay must be established, not depending entirely on chance, or the use it is put to. In its growth, three parts appear to be formed: one from the rising cone, which is the centre; a second on the outside; and a third, being the intermediate substance. These appear to have three stages of duration; for that which forms on the cone, I believe, makes the hair, and that on the outside makes principally the plate of whalebone: this, when got a certain length, breaks off, leaving the hair projecting, becoming at the termination very brittle: and the third, or intermediate * substance, by the time it rises as high as the edge of the skin of the jaw, decays and softens away like the old cuticle of the sole of the foot when steeped in water".

* Vide supra.

(2259). Other kinds of teeth, met with among Mammals, are composed of calcareous earths deposited in a nidus of animal matter, and consequently resemble bones in the hardness of their texture. In their simplest form these teeth consist of but one kind of material, called ivory; and in such cases there is no distinction into classes as in the human subject, every tooth being conical, and formed upon a simple pulp. Such are the teeth of the Porpoises (Delphinidce) and of the Cachalot Whales (Physeter.) The example selected to illustrate their structure and mode of growth is a preparation of a portion of the jaw of the Bottle-nose Whale (Delphinus tursio), contained in the Hunterian collection 1. From this it is seen (fig. 397) that each tooth of the Cetaceans in question is a hollow cone of ivory (a, b, c, d), which, on being split longitudinally, is found to contain a vascular pulp exactly filling up its internal cavity. It is upon the surface of this pulp that the ivory matter is produced and deposited, stratum inter stratum, within the tooth, thus gradually adding to its substance as growth proceeds. In animals possessing a dental apparatus of this description, Mr. Hunter observed that the teeth are not at first developed in the jaw, but appear to form in the gum upon the edge of the maxillary bones; and that they either sink into the jaw as they lengthen, or, as is more probably the case, the alveoli rise to enclose their roots as growth advances. It would moreover appear that these creatures do not shed their teeth, but that, as the jaw enlarges, new teeth are constantly produced from behind, while those towards the symphysis fall off, and their sockets become absorbed: thus the size of the teeth is made to keep pace with the increasing dimensions of the jaw 2. The exact number of teeth met with in any species of these Whales will evidently be uncertain.