46 



CEREBRAL DEVELOPMENT 



portions of tliis portion of the ancient Cephalaspian head^ 

 differ very considerably from those of the corresponding pai 



Fig. 11. 



a a 



CRANIAL BUCKLER OF COCCOSTEUS DECIPIENS. 



a, a, Points of attachment to the cuirass which covered the upper part 

 of the creature's body. 



in the modem cycloid one j but in their larger divisions, the 

 modern and the ancient answer bone to bone. Three osse- 

 ous plates in the Coccosteus, A, C, I, the homologues appa- 

 rently of the occipital, frontal, and nasal bones, range along 

 the medial line. The apparent homologues of the parietals, 

 B, B, occupy the same position of lateral displacement as the 

 parietals of the cod, and of so many other fishes. The pos- 

 terior frontals, F, and the anterior frontals, D, also occupy 

 places relatively the same, though the latter, which are of 

 greater proportional size, encroach much further, laterally and 

 posteriorly, on the superior frontal, C, C, 0, and sweep en- 

 tirely round the upper half of the eye-orbits, 2, 2. The ap- 

 parent homologue of the mastoid bone, E, which also occu- 



* This designation, is worthy of remark, as coinciding with Professor 

 Huxley's most recent researches. (See previous quotation.) He says 

 likewise, in a letter to me, *' Fishes such as Cephalaspis, Pteraspis (and 

 I may now add Coccosteus), present certain features of resemblance to the 

 Siluroids, which are Teleostean fish." — L. M. 



