DISSECTION OF A BONY FISH. 15 



white or pinkish brain. When this is exposed make out in 

 it the following parts, beginning in front : 



(1) The olfactory lobes tapering in front into the nerves 

 going to the nasal pits (p. 10). 



(2) Two rounded oval masses (cerebral hemispheres) 

 meeting in the middle line in front, and together constitut- 

 ing the cerebrum. 



(3) The 'twixt-brain, also two-lobed, but lying at a 

 lower level. 



(4) The large, paired, rounded optic lobes. 



(5) The unpaired cerebellum crowded in between the 

 optic lobes behind and extending back over the base of 



(6) the medulla oblongata, 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 ? 



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 numer- 

 ous 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. 10). 



(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. 



