MORPHOLOGY OF THE CEREBRAL CONVOLUIONS. 277 



Reference has been made to the only three conceivable theories which can be 

 held to account for the various cerebral depressions and elevations. According to 

 the first of these, which is advocated by Ecker and some others, the fissures and 

 convolutions are believed to be due to the effect of pressure ; the brain mass grow- 

 ing more rapidly than the containing bony cavity, the increased cerebral surface is 

 necessarily thrown into folds and depressions, the directions, relations, height, 

 breadth and depth of which must evidently depend upon the relative or differential 

 rates of growth in different regions of the brain-mass and its bony environment. A 

 study of the brain surface according to this view would, therefore, be really a me- 

 chanical problem involving the determination of the differential composition and 

 resolution of the component strains and pressures produced by brain growth as 

 compared with skull expansion. Undoubtedly many and, indeed, most of the 

 important fissures, those formed earliest in the history of development, are pro- 

 duced in this manner, and it is proposed in this paper to attempt to establish as 

 part of the morphological plan upon which the fissures and convolutions are built 

 up that this is really the case ; that these typical or foundation fissures are modi- 

 fied, turned aside, rendered more tortuous and complex by laws of growth peculiar 

 to different regions of the cerebral mass itself, and in this way to determine — to re- 

 peat a previous quotation from Ecker — "the law (or plan) 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 the brain and skull. Up to the 

 present time, however, we are far removed from such knowledge. At the farthest, 

 the the fossa Sylvii is open to an explanation from this point of view." It will be 

 shown that not only the fossa Sylvii but many other of the primary and fundamen- 

 tal fissures, those which lay down the groundwork or plan of the cerebral hemis- 

 phere, are produced in this way. 



The second theory depends for its explanation upon genetic principles having 

 their seat in the brain substance itself. This view is held by Pansch, who insists 

 ''that in Man and the apes there is in fact a natural system of the convolutions ; 

 that is. a practical division of the cerebral surface which does not depend upon 

 chance, but upon genetic principles, and that the convolutions owe their origin to a 

 difference in growth in certain portions of the surface." Bischoff, from his insistence 

 that all of the principal and primary furrows are surrounded at each extremity by 

 arched convolutions, and that they cannot according to his view be at an} T time ab- 

 sent, must also accept this theory as the explanation of the production of the de- 

 pressions and elevations of the cerebral surface. In treating of the relations of the 

 brain to the cranial bones he remarks: "I believe that in this way the brain may be 

 divided into principal parts or lobes." He declares, however, that we cannot take 

 this as a genetic relation, and that it cannot, therefore, be transferred to the relation 

 existing in animals or in childhood. We can. therefore, recognize from the rela- 

 tions of the surrounding bones to the different parts of the large brain^no principle 

 founded in the genetic relations of the two. Different, however, is the case in re- 



