THE STRUCTURE AND ACTIVITIES OF A FISH . i ?3 
largest pair of globular masses are the optic lobes. In 
front of these we find the cerebral lobes, corresponding 
to the cerebrum or front brain in man. Behind the 
optic lobes the cerebellum is situated. Sketch the brain 
showing all these parts, showing also the olfactory 
nerves extending to the nostrils, the optic nerves lead¬ 
ing to the eyes, the auditory nerves leading to the 
ear-sac with its “ear-stone,” and the spinal nerve 
extending along the back. 
The Bones of a Fish. Skeletons or parts of skele¬ 
tons can be easily prepared for laboratory use by soak¬ 
ing in hot water. Heads and backbones of large fish 
can be obtained without cost at the markets in most 
places. 
Fig. 134.—Skeleton of a Fish. 
With the skeleton of a fish notice the visceral cavity 
and the neural cavity. What is the relation of these 
cavities ? 
Notice the brain-cavity. Where was the brain con¬ 
nected with the spinal cord ? 
Do you find openings for nerves extending to ears, 
eyes, and nostrils ? 
Do you see how the skull is joined to the vertebral 
column ? 
