HO LOST El 



525 



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

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

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



A, Salmo salar, L. : longitudinal section through the head exposing the sense-organs, and 

 brain-cavity viewed from above (after Brnch). B, transverse section of the head of a young 

 Kalian trutla, L., in the region "i the fore-brain. C, D, and E, three diagrams showing the 

 development of the interorbital septum, a.c, auditory capsule ; al, alisphenoid ; a.n, auditory 

 nerve ; n.s.f, cavity for anterior semicircular canal ; h, optic lobe ; b.c, brain-cavity ; 6s, basi- 

 aphenoid ; c.w, cranial wall ; e, eye ; e.c, ethmoid cartilage ; epo, epiotic ; exo, exoccipital ; f.b, 

 fore-brain;//-, frontal; h, liyomandibular ; h.c, cavity for horizontal semicircular canal; i.s, 

 interorbital septum ; my, myotome ; n.e, nasal capsule ; 0.11, olfactory nerve ; op. n, optic nerve ; 

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

 capsule; pro, prootic : ptf, postfrontal ; r, cranial root: 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- 



