OF THE EARLIER VERTEBRATA. 59 



tals ranging, as in the skull of the carp, and in that of most 

 of the mammals, in their proper place in the medial line. 

 But the under surface of the cranium, armed, as on the upper 

 surface, with plates of bone, exhibited an arrangement still 

 more peculiar (fig. 21). In rectangular patches of palatal 

 teeth, its curious dart-like bone, placed immediately behind 

 these, and attached, as the dart-head is attached to the handle, 

 to a broad lozenge-shaped plate, with two strong osseous pro- 

 cesses projecting on either side, forms such a tout ensemble as 

 is unique among fishes. Even here, however, there may be 

 traced at least a shade of homological resemblance to the 

 bones which form the base of the osseous skull. The single 

 lozenge-shaped plate (A), with its dart-head, occupies the place 

 of the basi-occipital bone ; the posterior portion of the vomer 

 seems represented by a strong bony ridge, extending towards 

 the snout ; two separate bones, each bearing one of the an- 

 gular patches of teeth, correspond to the sphenoid bone and 

 its alse ; and, attached laterally to each of these, there is the 

 strong projecting bone, on which the lower jaw appears to 

 have hinged, and which apparently represents the lower part 

 of the temporal bone. Not less singular was the form of the 

 creature's under jaw (fig. 22). I know no other fish-jaw, 

 Fiff. 22. 



UNDER JAW OF DIPTERUS. 



whether of the recent or the extinct races, that might be so 

 readily mistaken for that of a quadruped. It exhibits not 

 only the condyloid, but also the coronoid processes; and, 



