GREGORY: FISH SKULLS 



153 



common with the Albulidse. In general appearance its slcull suggests relationships with 

 the Salmonidse. 



Salmonoidea (Salmon, Smelt, etc.) 



Salmonids. — -The typical salmon skull (Figs. 45-48) is probably retrogressive or psedo- 

 genetic in the high degree to which its endocranium has become cartilaginous; but it is 



de+h 



myodotne 



sp/io+ 



Fig. 47. Salmo sp. A. Lateral view of endocranium, with attached suspensorium and primary upper jaw. B. Median sag- 

 ittal section of endocranium, showing its largely cartilaginous nature. 



distinctly progressive in the fact that the supraoccipital is broadly in contact with the 

 frontals and has thrust aside the reduced parietals. Few if any of the numerous highly 

 peculiar features of the clupeid neurocranium are visible in the salmon. The ethmoid 

 cartilage is large, as well as the ectosteal ethmoid ("mesethmoid") above it. 



