694 Dynamic Theory. 



When a given tract expands as far as the brain case and the flexibility 

 of the adjacent organs will allow, it gets further room for growth by 

 doubling down into sulci grooves or fissures. Since these sulci occur in 

 the organs having the most vigorous growth, and since the growth is de- 



FIG. 372. 



FIG. 372. Brain of Prof . C. F. Gauss, the mathematician who died in 1854, aged 78. 

 Brain of average size, well formed and fully developed convolutions. Note the differ^ 

 ence in the details of the opposite sides. ( From Quain, after R. Wagner.) 



a, a, a. Superior, or first frontal convolution. 

 a ,a',a . S 



econd, or Middle 

 a". Third, or Inferior 



A, A. Ascending 



B, B. Ascending parietal 



b. Superior parietal lobule. 

 6". Inferior 



c. First, or Upper tempero-sphenoidal convolution. 



d. First, occipital 



d . Second, or Middle occipital 

 d". Third, or Lower 



I, I. Longitudinal fissure. r. Sulcus of Rolando. 



p. External parieto-occipital fissure, appearing nearer the back end than it really is, 

 owing to the position of the brain. 



termined by habit and education, and since these are not alike in any 

 two people, we must conclude that the difference in fissures and convo- 

 lutions between two brains is a sign of difference in education and habit 

 and their representative organs. The existence and increase of the fis- 

 sures is evidence that the organs begun in infancy from centers more or 

 less separated, have grown laterally till they have encroached upon each 

 other. 



There is undoubtedly a means of communication between different or- 



