188 



PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



instinctive reactions are controlled. In the matter of lami- 

 nation and distinct variations in size and appearance of the 

 strata of cells and fibers the human cortex shows a greater dif- 

 ferentiation than in the lower animals, and it is especially 

 characterized by a large development of what are known as 

 associational areas (p. 223), particularly in the frontal lobe. 

 In the third place, the central nervous system throughout the 

 vertebrates is constructed upon the same lines, a mechanism of 

 interconnecting neurons. There is a vast difference in the men- 



*' 





Fig. 85. Sections through corresponding parts of the cortex in: a, Man; 6, dog; 

 and c, mole, to show the greater separation of tne nerve cells in the higher animals. 

 (Bethe, after Nissl.) 



tal activity of a frog and a man, but the cortex of the cerebrum 

 shows a fundamental similarity in structure in the two cases. 

 In addition to the variations in stratification or lamination referred 

 to above one general distinction that comparative anatomy is able 

 to make is that in the higher animals the greater mental develop- 

 ment is associated with a greater complexity and richness in the con- 



