TEETH OF MONOPHYODONTS. 



277 



218 



m 



§A 



being nearly transverse to the axis of the skull. The subsidiary 

 plates are arranged in oblique series internal to the marginal ones. 

 Thus, if the upper jaw of one side of the skull of a Whale were 

 bisected transversely, the flat surface of a series of the baleen- 

 plates would be exposed, as in fig. 218, in which a is the superior 

 maxillary bone, b the ligamen- 

 tous gum, giving attachment to c 

 the horny base and body of the 

 chief baleen-plate, which termi- 

 nates in d, the fringe of bristles ; 

 e marks the smaller baleen-plates. 

 The base of each plate is hol- 

 low, and is fixed upon a pulp 

 developed from a vascular gum, 

 which is attached to a broad and 

 shallow depression occupying the 

 whole of the palatal surface of 

 the maxillary and of the anterior 

 part of the palatine bones, the 

 Whale being thus, like the 

 Echidna, an example of a mamma- 

 lian animal, which may be said to 

 have palatal teeth. The base of 

 each plate is unequally imbedded 

 in a compact sub-elastic sub- 

 stance, b, which is so much deeper 

 on the outer than on the inner 

 side, as, in the new-born whale, 

 to include more than one half of 

 the outer margin of the baleen-plate. This margin is shown at c, 

 fig. 218, and is continued down in a line dropped nearly vertically 

 from the outer border of the jaws. The inner margin of each plate, 

 d, slopes obliquely outward from the base to the extremity of the 

 preceding margin; the smaller plates decrease in length to the 

 middle line of the palate, so that the form of the baleen-clad 

 roof of the mouth is that of a transverse arch or vault, against 

 which the convex dorsum of the thick and large tongue, fig. 

 217, a, is applied when the mouth is closed. Each plate sends 

 off from its inner and oblique margin the fringe of moderately 

 stiff but flexible hairs, Avhich project into the mouth. These 

 present an obstacle to the escape of the small marine ani- 

 mals, 1 for the prehension and detention of which this singular 



1 Clio borcalis, Limacina arctica, and small pelagic Crustacea. 



Section of Upper Jaw, with Baleen-plates, of a 

 Whale {Balcenoptcra). 



