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Jaws and Teeth

jaw, lower, plate, figures and mass

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JAWS AND TEETH.' The mouth parts of the barracuda deserve attention both for them selves and because they do not seem to have been adequately described. The mouth is very large, being in length nearly half of the head and having a large gape. Together with this, the projecting lower jaw, the enormous canine teeth, the large glassy staring eyes, give the fish an aspect of ferocity which is not belied by its habits, as will be shown later. It has been fittingly compared to a bull-dog, and Saville-Kent (1893) notes that at Moreton Bay, Australia, it is called dingo because of "its formidable array of teeth." The lower jaw is longer than the upper, projecting notably as a conical fleshy mass of tissue which, if on the upper jaw, would form a decided snout. Dissection of this jaw in the fresh specimen revealed the following interesting structure: The rami of the mandible are as usual united at the apex by a mass of cartilage, but what is unusual is that this cartilage projects forward as a considerable lump which, covered by flesh and skin, gives the lower jaw the appearance shown in figures 3 and 4, plate n, and figures 7 and 8, plate m. For the dis sected jaw see figure 13, plate xv. It should be noted, however, that in cutting away the flesh and skin some of the cartilage was unwittingly removed, hence the projecting mass is not as great as in nature. This conical lump forms the terminal part of the rather thin fibrous lip of the lower jaw. This lip is freely movable and has, fastening it to the akin of the jaw, a number of short oblique back wardly trending slips of tissue. These allow free motion of this lip. For these structures see figures 4 and 8, plates n and m.

Turning now to the upper jaw, it is readily seen that the premaxil laries lie outside of and are separated from the maxillaries by a deep groove. In front, the symphysis of these bones is, like that of the lower jaw, covered by a mass of soft tissue. This mass, however, is much smaller than that of the lower jaw, does not form such a conical pro jection, and is comparatively thin and upturned. At the very point on the median line this is hollowed out into a deep pocket for the recep tion of the great fang of the lower jaw. To aid in the formation of this cavity, the terminal portions of both premaxillaries are hollowed out to the point of union to form a little bay. Viewed dorsally, the

maxillaries seem to lie above and (in the hinder region) outside of the premaxillaries, but in front they swing toward the median region. Viewed from below, the true situation is revealed; posteriorly they lie outside the premaxillaries, but about one-fourth the distance forward they cross over these bones and come to lie inside and are united by tissue in the region of the hinder group of great fangs on the premax illaries. Attached to each premaxillary is a thin fold of skin forming a less pronounced and less movable lip than is found on the lower jaw. These structures are seen in figures 7, plate m; and 11 and 12, plate iv.

The articulation of the upper jaw to the skull is entirely unique and hence worthy of description. The premaxillaries are non-protractile and are almost incapable of motion. The maxillaries, however, are so hinged onto the anterior end of the cranium as to allow the tip of the upper jaw to be raised in a vertical plane. This interesting articula tion is shown in figures 11 and 12, plate iv. The vomer has each shoulder beveled off dorsally and anteriorly, and in front there is a stout spine rounded off on the upper surface and the anterior end. The palatines send forward stout processes rounded in front, flattened below and especially on the inner edges. Between these two processes above and the projecting point of the vomer below there is seen a con siderable space, if one looks at the skull laterally. In a ventral view the maxillaries are seen to have just behind their symphysis a pair of pockets or recesses; a dorsal one as wide as long, and a shallow ventral one lying anterior to the other. The roof of the larger recess is made by the nasals, which are united by and imbedded in a mass of carti laginous material. The sides of this pocket are formed by two rounded backwardly and slightly inwardly projecting prominences of the maxil laries. Viewed from above, the anterior ends of the maxillaries, just outside the processes described, are hollowed out into shallow cavities whose use will be described below. Figures 11 and 12, plate iv, show these structures both from below and from above.

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