THE STPUCTUUE OF THE PIKE S SKULL. 



171 



unites with its fellow for a short distance, and so constitutes the 

 upper boundary of that foramen, shutting out the superior bone 

 from any share in its formation. Except in this point, it will be 

 observed that the three bones quite correspond with the ex-occi- 

 pitals and supra-occipital (S.O.) of Man. The ex-occipital (E.O.), 

 however, further differs from that of Man in that it is perforated 

 and not merely notched, by the foramen for the eighth pair, and 

 that it is produced in front of, and external to, this foramen, so 

 as to enter largely into the chamber which lodges the lower and 

 posterior part of the organ of hearing. Furthermore, there is no 

 perforation for any hypoglossal nerve, that nerve not being 

 represented in a distinct form in the fish. 



Fig. 70. — The basal and lateral bones of the skull of a Pike viewed from above. The squa- 

 mosal and the three periotic bones are left unshaded. P, the pituitary fossa. 



In the Pike, no bony wall separates the membranous laby- 

 rinth from the cavity of the skull, the periotic ossifications being 

 all situated, as they are when they first appear in Man, upon the 

 outer side of the capsule of the labyrinth : and this capsule is 

 still less complete than that of the human foetus, seeing that 

 its inner wall is not even cartilaginous, but remains in the 

 condition of membrane. Notwithstanding the comparatively 

 incomplete condition of the periotic bones of the fish, however. 



