THE TARPON 



175 



A thick oily choroid gland 2iA to 3 m.m. in thickness is found 

 at the posterior pole and thinning gradually until it ceases at 

 the ora seratta. The optic nerve somewhat flattened bends 

 sharply on leaving the eyeball crossing to reach the brain. 



The sclerotic in its posterior portion becomes membranous. 

 The optic nerve is hidden in a mass of white oily tissue with 

 the immense extra ocular muscles exerting pressure as they 

 move the flattened eyeball. 



The muscles of the eyeball are exceedingly heavy and strong, 

 the one passing under the eyeball having at its insertion a 

 diameter of 10 m.m. and a thickness of 5 m.m. The change of 

 focus is accomplished by a change of position of the crystal- 

 line lens and vitreous, doubtless through the pressure of the 

 extra ocular muscles. 



Section through the eyeball showing the relative position of 

 the cornea and lens with the cup-shaped additional cavity for 

 the regulation of pressure on motion of the lens and vitreous. 



