WHALES. 313 



anterior and obliquely backwards in the posterior plates, and the 

 inner margin at the basal part of the posterior plates is slightly 

 curved towards the back part of the mouth, to which the bristly 

 terminations of these parts of such plates are directed, thus pre- 

 senting an additional obstacle to the escape of the small marine 

 animals(l), for the prehension and detention of which, this singular 

 modification of the dental system is especially adapted. 



The interspaces of the free extremities of the baleen-plates^ 

 which, from the oblique position of their fringed internal margins, 

 are only visible by raising the large lip and looking on the outer 

 part of the series, are in general equal to five or six times the 

 thickness of the plates themselves ; the external line of the plate 

 is broken by the outward projection (2) of the base of the free 

 portion of each plate, at least in the dry subject. In the specimen 

 above alluded to, the pulp-cavity at the base of each principal tooth 

 presented the form of a narrow, transversely-elongated fissure, from 

 four to five lines in depth in the larger plates. The bases of the 

 baleen-plates do not stand far apart from one another, but the 

 anterior and posterior walls of the pulp-fissure are respectively con- 

 fluent with the contiguous divisions of the bases of the adjoining 

 plates at their thin and extreme margins, which by this confluence 

 close the basal end of the interspace of the baleen-plates, which 

 interspace is occupied more than half-way down the plate, by the 

 cementing substance or gum. Thin layers of horn in like manner 

 connect the contiguous plates, and may be traced extending in 

 parallel curves with the basal connecting layer across the cementing 

 substance, as shown in the diagram, PI. 76, fig. 6, c. 



The baleen-pulp (indicated by the dotted line, at a) is situated 

 in a cavity at the base of the plate, like the pulp of a true tooth ; 

 whilst the external cementing material maintains, both with respect 

 to this pulp and to the portion of the baleen-plate which it de- 



(1) Clio horealls, Limacina, and small pelagic Crustacea. Before the naturalists of the 

 Arctic expeditions had determined the nature of the food of the true Baleence, John Hunter had 

 stated " I do suppose the fish they catch are small when compared with the size of the mouth." 

 On the Structure and Economy of Whales, Phil. Trans. 1787, p. 397- 



(2) The letter a is placed near the line of termination of the baleen matrix in fig. 4, called 

 the "bead," by Hunter, Phil. Trans. 1787, p. 307. V 



