Pisces. 



79 



25 . Observe the white spinal cord in the tube formed by the neural 

 arches above the bodies of the vertebrae. This is the nerve tube, or 

 neural tube ; note also the blood tubes in the corresponding hemal 

 tube, below. 



THE BRAIN OF THE FISH. 



Cut off the head ; clear away the muscles at the back of the 

 head ; carefully slice off the top of the skull with a strong, sharp 

 knife ; with extreme care cut away the roof of the brain cavity ; 

 a mass of loose, gray tissue covers the brain, which is of a white 

 or pinkish color; cautiously pick away this loose tissue, using a 

 small syringe, or medicine dropper, to wash away the loosened 

 matter. Make out the following parts of the brain, beginning at 

 the posterior end : 



1. The cut-off end of the spinal cord. 



2. The widened part of the spinal cord, where it passes under 

 the hinder part of the brain, is the spinal bulb. 



3. The hinder, undivided part of the brain is the cerebellum. 



4. In front of the cerebellum are the two large, rounded optic 

 lobes, forming the widest part of the brain. 



5. In front of the optic lobes are two oval masses which meet 

 in the middle line; these are the cerebral hemispheres, and to- 

 gether they constitute the cerebrum. 



6. Observe the olfactory lobes tapering forward in front of the 

 cerebral hemispheres ; from these trace the olfactory nerves to 

 the nasal cavities. 



Make a drawing of the brain as seen from above, naming all 

 these parts. Cut open one of the optic lobes and note that it is 

 hollow ; push the eyes outward and find a white cord extending 

 inward and backward from each. These are the optic nerves. 



THE MUSCLES OF THE EYE. 



i. Cut away the upper part of the eye sockets and find in each 

 a muscle extending outward and backward from the anterior part 

 of the socket to the top of the eyeball. This is the superior 

 oblique muscle, 



