THE DOGFISH 



3 6 7 



merit of the organs of the head causes the distribution to 

 differ in detail. The olfactory nerves are a bunch of fine 

 threads which pass from the olfactory lobes of the 

 brain into the adjoining olfactory organs. The optic 



Fig. 263. — The brain of a dogfish, in ventral view. 



cer., Cerebrum ; in/., return limb of infundibulum, sometimes regarded as the 

 pituitary body ; /.*'., lobi inferiores ; m.o., medulla oblongata; olf.l., olfactory 

 iobe ; ol/.o., olfactory organ; op., ophthalmic branches of fifth and seventh 

 nerves ; sp.c. , spinal cord ; s.z>. , lateral lobe o( saccus vasculosus ; s.v'., median 

 lobe of the same ; II.-X., cranial nerves. 



nerves pass from the lower surface of the thalamen- 

 cephalon, each through the optic foramen of the opposite 

 side, to the eyeballs, crossing in a chiasma below the 

 brain. The third or oculomotor nerve of each side, arising 

 from the ventral surface of the mid-brain, passes outwards 



