ANATOMY AND PHARMACOLOGY OF EYE 395 



The eyes saved previously from dogs may be used for 

 dissection, or eyes from hogs or cattle may be secured (in 

 weak formalin solution) from the slaughter house. 



Dissect away the fascia from the outside of the eye-ball 

 and isolate and identify the extrinsic muscles. Are there 

 any variations in these in different species of animals! 

 What is the innervation of these muscles"? 



Isolate the optic nerve and follow it to the sclera. Dis- 

 sect off the extrinsic muscles and free the eye from fascia. 

 Do you have a right or a left eye? Locate on the eye-ball a 

 point directly outside the area which should be occupied by 

 the fovea centralis. Do the lower animals possess this 

 structure? What is its function? Over this area cut a win- 

 dow about one-eighth inch square in the sclerotic down to 

 the choroid. Hunt for the fibers of the ciliary nerves which 

 pass forward in the interspace between the sclera and the 

 choroid. In the normal animal what reactions would fol- 

 low electrical stimulation of these fibers? With care en- 

 large the opening in the sclerotic a little and then dissect 

 away the choroid which forms the floor of the opening. 



Use great care not to penetrate the retina which will be 

 exposed when the choroid is removed. If the eye has not 

 been long in the formaldehyde or alcohol the cornea and 

 lens may still be transparent enough to allow an image to 

 be formed on the retina (this is best shown in fresh eyes). 



Take a sheet of brown wrapping paper a foot square and 

 roll it into a tube with an opening just large enough to hold 

 the eye at one end. Place two rubber bands around the 

 tube to prevent unrolling. The eye is placed in the end of 

 the tube with the opening in the sclerotic and choroid coats 

 turned outward, i.e., the cornea and lens are directed to 

 look through the tube. Point the open end of the tube to- 

 ward an incandescent light or bright window and watch 

 carefully in the exposed area at the back of the eye for an 

 image of the light or window. If you detect any image 

 state fully its characteristics and peculiarities. 



