OF THE EARLIER VERTEBRATA. 45 



tbe occipital, and one-half the two temporal bones. And 

 whereas in man, and in most of the mammals, there are four 

 of these placed in the medial line, — the four which, accord- 

 ing to the assertors of the vertebral theory, form the spinal 

 crests of the four cerebral vertebrse, — in the cod there are but 

 three. The super-occipital bone, A (fig. 1 0), pieces on to the 

 superior frontal, C, C, C ; and the parietals, B, B, which in 

 the human subject form the upper and middle portions of 

 the cranial vault, are thrust out laterally and posteriorly, and 

 take their places, in a subordinate capacity, on each side of 

 the super-occipital. This is not an invariable arrangement 

 among fishes. In the carp genus, for instance, the parietals 

 assume their proper medial place between the occipital and 

 frontal bones ; but so very general is the displacement, that 

 Professor Owen regards it as characteristic of the great ich- 

 thyic class, and as the first example in the vertebrata, reckon- 

 ing from the lower forms upwards, of a sort of natural dislo- 

 cation among the bones, — "a modification," he remarks, 

 "which, sometimes accompanied by great change of place, 

 has tended most to obscure the essential nature of parts, and 

 their true relations to the archetype." 



Of all the cerebral bucklers of the first ganoid period, that 

 which best bears comparison with the cranial front of the cod 

 is the buckler of the Coccosteus (fig. 11.) The general pro- 



son of the divisions of the ancient ganoid cranium with those of the 

 craniums of existing fishes, the points at issue between the two great na- 

 turalists are not involved, otherwise than as mere questions of words. 

 The matter to be determined, for instance, is not whether plate A in the 

 sktdls of the cod and Coccosteus be the homologue of a part of the occipi- 

 tal or that of a part of the parietal bones, but whether plate A in the 

 Ooccosteus be the homologue of plate A in the cod. The letters em- 

 ployed I have borrowed from Agassiz's restoration of the Coccosteus; 

 whereas the figures intimate divisions which the imperfect keeping of 

 the specimens on which the ichthyologist founded did not enable him to 

 detect. 



