546 



COMPARATIVE PHYSIOLOGY. 



Oblique 

 move- 

 ments. 



f Elevation with adduction. . Rectus superior and intemus, 



with obliquus inferior. 

 Depression with adduetion.Rectus inferior and intemus, 



with obliquus superior. 

 Elevation with abduction. . Rectus superior and externus, 



with obliquus inferior. 

 Depression with abduction.Reetus inferior and externus, 



with obliquus superior. 



What is the nervous lOechanism hy which these " associ- 

 ated " moYements of the eyes are accomplished ? It has heen 



found, experimental- 

 ly, that when different 

 parts of the corpo- 

 ra quadrigemina are 

 stimulated, certain 

 movements of the eyes 

 follow. Thus stimu- 

 lation of the right side 

 of the nates leads to 

 movements of hoth 

 eyes to the left, and 

 the reverse when the 

 opposite side is stimu- 

 lated ; also, stimular 

 tion in the middle line 

 causes convergence 

 and downward move- 

 ment, etc., with the 

 corresponding move- 

 ments of the iris. 

 Since section of the 

 nates in the middle 

 line leads to move- 

 ments confined to the 



Fio. 394.— Diagram intended to illustrate action of eye of the Same side, 



extrinsic ocular muscles (after Fick). The heavy ,, , , , 



lines represent the muscles of the eyeball, and the trie center WOUlQ ap- 



flne lines the axes of movement. ^^^ ^ ^^ double. 



However, it may be that the cells actually concerned do not lie 

 in the corpora quadrigemina, hut helow or outside of them. The 

 localization is as yet incomplete. In many groups of animals, 

 including the solipeds, ruminants, and Carnivora, there is a 

 posterior rectus or retractor oculi by which the eye may be 



