THE BRAIN 



687 



is formed. This, in man, is greater than all the rest of the brain. 

 They enclose the expansions of the central neural canal, known as 

 the lateral ventricles. The olfactory bulbs are outgrowths from this 

 part of the brain. 



FIG. 414. SHOWING THE POSITION ASSUMED BY FROG AFTER REMOVAL OF CEREBRAL 



LOBES. 



Voluntary movement is lost. When the mid-brain is removed the frog cannot 



control its movements. 



The cerebral hemispheres are the latest outgrowths to be developed, 

 and are especially marked in the primates and man. In the lower 

 animals, on the other hand, the thalamencephalon and mesencephalon 

 are more developed, parts which are connected with primitive sensa- 

 tions and emotions rather than judgments. 



FIG. 4)5. To SHOW THE DISSECTION FOU REMOVAL IN THE FKOG OF THE FORE- BRAIN 

 (a) AND THE OPTIC LOBES (b). 



After removal of these the flap of skin may be stitched in position again. 



In the lower vertebrates, the brain is formed b} the enlargement 

 of the anterior end of the spinal cord, and by the widening and division 

 of the central canal to form ventricles. Upon this primitive brain- 

 stem are developed swellings in connection with the senses of most 

 importance to these lower forms namely, the sense of smell and the 

 sense of sight. Usually, one or other of these is predominantly 



