518 



ELEMENTARY PHYSIOLOGY 



to make connection with the brain, as the optic 

 tracts. 



These are connected, as already stated, with the hinder 

 part of the optic thalami and with the anterior pair of 

 corpora quadrigeuiina. At the chiasma the fibres of the 

 optic nerves undergo a remarkable partial decussation. 

 The fibres from each half of the retina nearest to the nose C70ss 



Fio. 166.— A Diagram illustkating the Superficial Origin of the 

 Cranial Nervks. 



H, the cerebral hemispheres ; C.S. corpus striatum ; Tk. optic thalamus ; 

 P. pineal body ; Ft. pituitary body ; C.Q. corpora quadrigemiiia , Ch. cere- 

 bellum ; M. medulla oblongata ; /. — XJI. the pairs of cerebral nerves ; 

 Sp. 1, Sp. 2, the first and second pairs of spinal nerves. 



over to the opposite side of the brain ; the fibres from the 

 other half of each retina pass into the brain without 

 crossing. Hence the right optic tract contains the fibres 

 from tlie nasal half of the left retina and from the other 

 or temporal half of the right retina, and similarly the 

 left optic tract is made up of the fibres of the temporal 



