MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 249 



psychical brain organs, rests in great part in the hands of physicians. Only by accurate 

 observations of patients, in connection with the most careful autopsies, can we gradu- 

 ally arrive at some knowledge of the physiological meaning of the single convohitions 

 upon the cerebral surface." Yet he remarks, further on, in speaking of the devel- 

 opment of the convolutions in the foetus : " this is also the only way to learn this 

 law of the formation of the convolutions, that is, the formation of the convolutions 

 as a necessary consequence of certain mechanical processes in the growth of brain 

 and skull. Up to the present time, however, we are far removed from such a knowl- 

 edge. At the farthest, the fossa Sylvii is open to an explanation from this point of 

 view." Now, if the convolutions are produced by a process of mechanical packing, 

 how can we expect that they will represent localized centres of different faculties ? 

 What connection can an arrangement of cerebral matter produced by " mechanical 

 processes in the growth of brain and skull " have with the localized position of certain 

 functional cells ? The two views taken together, seem incompatible. Either the fac- 

 ulties are not localized in special convolutions, or, if they be considered as represent- 

 ing these districts, then must the} 7 also be regarded as produced structurally by 

 processes of growth taking place within the brain mass alone, and at most merety 

 modified in shape and position by the presence of its bony environment. The great 

 regularity of folding, following, as we shall endeavor to show, a definite symmetrical 

 plan related to the structure of the hemispherical mass would seem to indicate 

 definite processes of brain-growth modified hy relations of growth to the containing 

 cavity. The following facts seem also to show that the convolutions and fissures, 

 at least the typical ones, are not produced by a species of mechanical packing alone. 

 Marshall, in an interesting paper, l has described and figured the brains of 

 two idiots of European descent. In it he shows that all of the principal fissures and 

 convolutions are present, only in a simpler condition and somewhat distorted. No 

 new fissures were found. Now, if fissures are dependent solely on gross mechanical 

 causes, should we not expect more than a mere distortion ? One has but to 

 examine the drawings given by Marshall to see what immense differences exist 

 in the mechanical conditions of growth between this and the normally developed 

 brain. So great has been the interference with normal growth that even the cor- 

 pora striata and thalami optici were found distorted. The cerebellum was pushed 

 up almost to a level with the cerebral hemispheres and the whole aspect of 

 the cerebrum changed. It would seem in a case like this that if fissures be 

 the result of merely gross mechanical processes of growth between the brain and 

 skull alone, we ought to find some distinct and separate fissures produced, instead 

 of a mere distortion and pushing out of place of fissures which are found in the 

 normally developed brain. 



Reasons will be given farther on, deduced from the manner of arrangement of 

 the convolutions not only in the Primates but in other animals, for considering 

 that the hemispheres of the cerebrum should be looked upon as nervous buds, 



1 On the Brain of a Bushwoman and Two Idiots, etc. Phil. Trans., London, 1864. 



