ITS STKUCTURE, BULK, AND ASPECT. 71 



« The inner surface of the cranial buckler of Asterolepis (fig. 

 29), — that which rested on the cartilaginous box which form- 

 Fig. 29 



INNER SUEPACE OF CRANIAL BUCKLEE OP ASTEBOLEPIS. 



(One-fifth nat. size, linear.) 



ed the creature's interior skull, — stands out in bolder relief 

 from the stone than its outer surface, and forms a more pic- 

 turesque object. Like the inner surfaces of the bucklers of 

 Coccosteus and Pterichthys, but much more thickly than these, 

 it was traversed by minute channelled markings, somewhat 

 resembling those striae which may be detected in the flatter 

 bones of the ordinary fishes, and which seem in these to be 

 mere interstices between the osseous fibres. And in the 

 plates, as in the bones, they radiate from the centres of ossi- 

 fication, which are comparatively dense and massy, towards 

 the thinner overlapping edges. These radiating lines are 

 equally well marked in the cerebral bones of the human foetus. 

 The three converging ridges on the outer surface we find on 

 the inner surface also, — the lateral ones a little bent in the 

 middle, but so directly opposite those outside, that the thick- 



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