BONY-FISH. 29 



(5) The unpaired cerebellum crowded in between the 

 optic lobes behind and extending back over the base of- 



(6) the medulla oblongqta, also unpaired, which in 

 turn tapers into the spinal cord. 



Draw the brain from above, three times the natural 

 size, naming the parts. 



Cut off the tops of the various regions of the brain. Do 

 you find cavities (ventricles) in any of them? Can you 

 find any nerves going from the brain? 



If no prepared skull is available, boil the head of another 

 fish for a few minutes, and then pick away the flesh as 

 far as possible with the forceps, taking care not to pull 

 any of the bones from their proper positions. This will 

 expose the skull, composed of numerous bones. See that 

 these can be grouped in the following regions: 



(1) The opercular apparatus, consisting of the several 

 bones composing the gill-cover (p. 24). 



(2) The facial portion, made up of the jaws and parts 

 connected with them; numerous small bones around the 

 eye, etc. See how the lower jaw is suspended from the 

 skull. Does anything like this occur in man? 



(3) The cranium, consisting of a number of bones 

 which form a box to enclose and protect the brain. 



