188 ON THE STRUCTURE OF THE SKULL. 



these are not anchylosed with the opisthotic bones),* the vomer, 

 and the parasphenoid. 



The bones which, as ossifications of the substance of the 

 cartilaginous cranium itself, are not thus separable, are the basi-, 

 ex-, and supra-occipitals, the three periotic bones, the ali- 

 sphenoids, the ba si-sphenoid, the post-frontals, the pre-frontals, 

 the bones 3.3 (Figs. 69 and 73). 



Thus, in a certain sense, the adult skull of the Pike may be 

 said to represent, in a persistent form, a condition of the skull 

 which is transitory in 31 an. 



Let the sides of the human foetal cartilaginous cranium grow 

 up and unite in the roof of the skull ; let the pre-sphenoidal, 

 ethmoidal, and internasal portions be greatly elongated ; let no 

 distinct ossification take place in the pre-sphenoidal and orbito- 

 sphenoidal regions, or in the part answering to the lamina 

 perpendicularis, while the basi-sphenoidal ossification remains 

 very small, and that cranium would put on the most important 

 and striking characters of that of the Pike. 



* How far the bone which I have marked Sq. in the skulls of Fishes is really a 

 membrane bone and the homologue of the squamosal of Keptiles, Birds, and 

 Mammals, is a question which needs thorough re-investigation. Mr. Parker is of 

 opinion that it is really a cartilage bone and the homologue, not of the squamosal, 

 but of an independent ossification, which he finds well developed in the periotic 

 Capsule of the Mole and Shrew, and terms the "pterotic." 



