HOLOSTEI 



325 



the cavum cranii, and piercing the prefrontal ; Hydrocyon, whose 

 nerves are longer and crossing the front of the orbit, has the 

 bulbus further back ; and finally, Erithrinus, with sessile bulbs, has 



A. 



pmx 



A, Salmo s<tlar, L. ; longitudinal sectioTi through the head exposing the sen 

 brain-cavity viewed from above (after Bruch). B, transverse section of the lit 



Salmo trutta, L., in the region of the fore-brain. 



osp, orbitosphenoid ; p, palatine ; pf, prefrontal ; pmx, preinaxilla ; p.o, ossification of optic 

 capsule ; pro, prootic ; ptf, postfrontal ; r, cranial roof ; s.o, superior oblique muscle ; s.r, 

 superior rectus muscle ; tr, trabecula. 



olfactory nerves passing out of the orbitosphenoid freely across the 

 orbit. The septum in the Gadiformes, on the other hand, is formed 

 below the brain-case, and the narrow brain-cavity is continued for- 



