FEOG 257 



and in that section whicli contains the outer half 

 study the pupil. Why is the pupil black? From 

 the inner section remove the vitreous humor, 

 and back of it find a delicate membrane, the 

 retina, covering the choroid. Look also for the 

 point of entrance of the optic nerve, the blind 

 spot. 

 Make a drawing showing the eye in antero-posterior 



section ; another to show the layers of membrane in the 



posterior half of the eye. 



h. The ear. — The parts of the internal ear may best 

 be dissected in preserved specimens which have 

 been macerated in a mixture of sixty per cent, 

 alcohol, to which a few drops of nitric acid have 

 been added. Leave the specimen in the mixture 

 until the muscles and bones assume a translucent 

 appearance, then, with forceps, pick away the 

 skin and muscles surrounding the auditory cap- 

 sule, tear off the top of the latter, which now has 

 the appearance and consistence of cartilage, and 

 within will be found the membranous laby- 

 rinth, which appears as a small white nodule, to 

 which are attached grayish pigmented parts. 

 Float the labyrinth into water in a watch-glass 

 and examine it with a lens. The white portion, 

 or vestibule, consists of two parts separated 

 by a constriction, the lower part being the sac- 

 culus and the upper the utriculus. From the 

 upper arise the three semicircular canals, 

 each of which bears at its base an enlargement, 

 the ampulla. Endeavor to trace the connec- 

 tions of the auditory nerve. 



Make a drawing showing the relation of these parts. 

 17 



