70 THE MICROSCOPE. May 



olfactory lobes, cerebral hemispheres, optic lobes, cere- 

 bellum and medulla oblongata. The brain is situated 

 between the eyes and is protected by a case of cartilage, 

 and above this by two long, thin and narrow bones. 



The olfactory lobes being anterior, the other parts 

 follow in the order named. The olfactory lobes are two 

 in number, right and left olfactories, and connected with 

 the nostrils by the olfactory nerves. The optic lobes, 

 right and left, as on the central hemispheres also, have 

 connection with the eye through the optic nerves. 



The eyeball is nearly spherical, and movable in its 

 orbit to a slight degree. The pupil of the eye is the 

 central opening of the iris, which is a pigmented dia- 

 phragm stretching across the interior of the eyeball, and 

 about one-quarter the distance from the front of the eye 

 to the back. In front of the pupil is the transparent 

 cornea, and between this and the iris is the aqueous 

 humour, a transparent watery substance. Immediately 

 back of the pupil is the crystalline lens, bi-convex, and 

 surrounded by muscles which can render the lens more 

 or less convex. 



The back of the eye-ball is covered with a silvery 

 membrane, the sclerotic coat. Within this is the dark 

 choroid coat. The optic nerve enters a little to one side 

 of the back of the eye and spreads over the inside of the 

 eye forming the sensitive retina. The chamber back of 

 the crystalline lens is filled by the vitreous humour, a 

 transparent jelly-like substance. 



The optic lobes are covered by the pia mater ; a thin 

 pigmented membrane. The cerebellum is a single mass 

 slightly constricted along the median line from front to 

 back. The medulla oblongata is a little beneath the 

 cerebellum, and extends posterially to the spinal canal, 

 where it becomes the spinal cord. 



9, The Spermaries are two large, white bodies, situ- 

 ated in the back part of the body cavity, distinguished 



