548 



SCIENCE. 



[N. S. Vol. XVIII. No. 461. 



especially with the convolutions of the 

 cerebral hemispheres. 



If a cast be taken of the cranial cavity 

 and compared with the brain which had 

 previously been carefully hardened in situ 

 before removal, it will be found that the 

 cast not only corresponds in its general 

 form to that of the brain, but shows a con- 

 siderable number of the cerebral fissures 

 and convolutions. This molding of the 

 inner surface of the skull to the adjacent 

 portions of the cerebral hemispheres is 

 usually much more marked at the base and 

 sides than over the vault. Since the 

 specific gravity of the brain tissue is 

 higher than that of the cerebro-spiual fluid, 

 the cerebrum tends to sink towards the 

 base and the fluid to accumulate over the 

 vault; hence probably these differences 

 admit of a simple mechanical explanation. 

 Except under abnormal conditions, the 

 amount of cerebro-spinal fluid between the 

 skull and the cerebral convolutions is so 

 small that from a cast of the cranial cavity 

 we can obtain not only a good picture of 

 the general shape and size of the higher 

 parts of the brain, but also various details 

 as to the convolutionary pattern. This 

 method has been applied with marked suc- 

 cess to the determination of the characters 

 of the brain in various fossil lemurs by 

 Dr. Forsyth Major and Professor R. Burek- 

 hardt, and Professor Gustav Sehwalbe has 

 made a large series of such casts from his 

 craniological collection in Strassburg. The 

 interesting observations by Sehwalbe* on 

 the arrangement of the 'impressiones 

 digitatae' and 'juga cerebralia,' and their 

 relation to the cerebral convolutions in 

 man, the apes and various other mammals, 

 ' have directed special attention to a very 

 interesting field of inquiry. As is well 



* ' Ueber die Bezieliungen zwischen Innenform 

 unci Aussenform des Schadels,' Deutsches Archiv 

 fiir Iclinische Medicin, 1902. 



known, the marked prominence at the base 

 of the human skull, separating the anterior 

 from the middle fossa, fits into the deep 

 cleft between the frontal and temporal 

 lobes of the brain, and Sehwalbe has 

 shown that this ridge is continued— of 

 course in a much less marked form— along 

 the inner surface of the lateral wall of the 

 skull, so that a east of the cranial cavity 

 presents a shallow but easily recognized 

 groove corresponding to the portion of the 

 Sylvian fissure of the brain separating the 

 frontal and parietal lobes from the tem- 

 poral lobe. Further, there is a distinct de- 

 pression for the lodgment of the inferior 

 frontal convolution, and a cast of the 

 middle cranial fossa shows the three ex- 

 ternal temporal convolutions. 



We must now turn to the consideration 

 of the relations of the outer surface of the 

 cranium to its inner surface and to the 

 brain. This question has engaged the at- 

 tention of experts as well as the 'man in 

 the street' since the time of Gall and 

 Spurzheim, and one might naturally sup- 

 pose that the last word had been said on 

 the subject. This, however, is far from be- 

 ing the ease. All anatomists are agreed 

 that the essential function of the cranium 

 is to form a box for the support and pro- 

 tection of the brain, and it is generally con- 

 ceded that during the processes of develop- 

 ment and groAvth the form of the cranium 

 is modified in response to the stimulus 

 transmitted to it by the brain. In fact, it 

 is brain growth that determines the form 

 of the (*ranium, and not the skull that 

 molds the brain into shape. This belief, 

 however, need not be accepted without some 

 reservations. Even the brain may be con- 

 ceived as being influenced by its immediate 

 environment. There are probably periods 

 of development when the form of the brain 

 is modified by the resistance ofl'ered by its 

 coverings, and there are certainly stages 



