390 



ELEMENTARY ANATOMY. 



[LESS. 



Finally, each eyeball may be supported at the end of a 

 long outwardly projecting pedicle, as in the. Shark which on 

 this account is called " Hammer-headed." 



21. The so-called olfactory 

 and optic nerves are thus not 

 really nerves, but prolonga- 

 tions and outgrowths of the 

 very brain itself; the other 

 so-called cranial nerves (ex- 

 cept a part of one, which part goes to the internal ear) are 

 properly thus designated. 



The THIRD AND FOURTH NERVES (Fig. 324) arise from the 

 mid-brain, and go respectively the first to all the orbital 

 muscles except the upper oblique and the outer rectus ; the 

 second, to the upper oblique orbital muscle. Both these 

 nerves traverse the spheno-orbital fissure. 



FIG. 343. HAMMER-HEADED SHARK. 



FIG. 344. DIAGRAM ILLUSTRATING THE ARRANGEMENT OF THE PARTS OF 

 THE BRAIN AND THE ORIGIN OF THE NERVES. 



//, the cerebral hemispheres ; CS, corpus striatum ; T/i, optic thalamus ; P, 

 pineal gland ; Ft, pituitary body ; CQ, corpora quadrigemina ; Cb, cere- 

 bellum ; M, medulla oblongata ; /. XII., the pairs of cerebral nerves ; Sp l 

 and Sp 2 , the first and second pairs of spinal nerves. 



The SIXTH NERVE arises from the base of the brain just 

 in front of the medulla oblongata, and goes through the 

 same fissure to the outer rectus muscle of the orbit. 



