472 



THE BRAIN. 



numerous and deeper the fissures upon the surface of a brain, the greater 

 is the amount of gray substance which it contains. 



Although the cerebral fissures and convolutions are never all precisely 

 the same in any two brains, nor even exactly symmetrical in the two 

 hemispheres of a single brain, yet the principal ones are sufficiently 

 constant to be regarded as essential features of the organ ; and the 

 remainder, while varying within certain limits, exhibit a general arrange- 

 ment which is characteristic of the species of animal to which they belong. 

 In man they attain a very high degree of development ; and their nomen- 

 clature is important as enabling us to recognize different parts of the 

 cerebral surface. 



PLAN OF THE FISSURES AND CONVOLUTIONS OP THE HUMAN BRAIN. The 

 fissures are designated by letters, the convolutions by numbers. S. Fissure of Sylvius; a. 

 Anterior ascending branch; b. Posterior horizontal branch. E. Fissure of Rolando. P. 

 Parietal fissure. 1. First frontal convolution. 2. Second frontal convolution. 3. Third 

 frontal convolution. 4. Anterior central convolution. 5. Posterior central convolution. 

 6. Supra-Sylvian, or supra-marginal convolution. 7. Superior temporal convolution. 8. 

 Angular convolution. 9. Middle temporal convolution. 10. Inferior temporal convolution. 

 11. Upper parietal convolution. 12. Occipital convolutions. 



Next in importance to the great longitudinal fissure, which separates 

 the two hemispheres upon the median line, is the Fissure of Sylvius (S). 

 This is a much deeper cleft than the others, and exists, according to 

 Prof. Wilder, in the brains of all animals where the cerebral surface is 

 fissured at all. In the human foetus it is the first to appear, being visi- 

 ble as early as the third month ; and in the adult it forms a basis for 



