60 Papers from the Department of Marine Biology. 



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 in. For the dis- 

 sected jaw see figure 13, plate iv. 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 skin 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 in. 



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 in; 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 



