54 CEREBRAL DEVELOPMENT 



exhibits its true form. It consists of two main divisions, 

 occipital (A) and frontal (C, fig. 1 6) ; and in each of these 



rig. 17. 



CEANIAL BUCKLER OF DIPLOPTEBUS. 



we find a pair of smaller divisions, with what seem to be in- 

 dications of yet further division, marked, not by lines, but 

 by dots ; though I have hitherto failed to determine whether 

 the plates which these last indicate possess their independ- 

 ent centres of ossification. Not unfrequently, however, has 

 the comparative anatomist to seek the analogues of two bones 

 in one ; nor is it at least more difficult to trace in the faint 

 divisions of the cranial buckler of the Diplopterus, the ho- 

 mologues of the occipital, frontal, parietal, and nasal bones, 

 than to recognise the representatives of the carpals of the 

 middle and ring finger in man in the cannon bone of the 

 fore leg of the ox. I may mention in passing, that the little 

 central plate of the frontal division (1, fig. 16), which so 

 nearly corresponds with that of the Osteolepis^ occurred, 

 though with considerable variations of form and homology, 

 and some slight difference of position, in all tbe ganoids of 

 the Old Red Sandstone whose craniums were covered with 

 an osseous buckler, and that its place was always either im- 



