650 THE DEVELOPMENT OF SKULL AND BKAINS. 



nervous system, and hence need special protection. They are not, 

 however, concerned with the .regulation of complicated voluntary 

 movements, the reception and storage of sensory impressions from 

 lower centers, and the activity of the various mental processes. These 

 functions we must associate with the higher parts of the brain, and 

 especially with the convohitions of the cerel)ral hemispheres. 



If a cast he taken of the cranial cavity and compared with the brain 

 wdiich had previously been carefully hardened in situ l)ef()re removal, 

 it will be found that the cast not only corresponds in its general form 

 to that of the brain, but shows a considerable number of the cerebral 

 fissures and <'onvolutions. This molding of the inner surface of the 

 skull to the adjacent portions of the c(;rebral hemispheres is usually 

 nmeh more marked at the base and sides than over the vault. Since 

 the spcM'itic gravity of the l)rain tissue is higher than that of the 

 cerebro-spinal Huid, the cerel)rum tends to siidv toward the base and 

 the fluid to accunndate over the \ault: hence probably these diti'er- 

 ences admit of a simple mechanical (wplanation. Except luider abnor- 

 mal conditions. th«> amount ot" cerebro-sijlnal 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 })icture of the general shape 

 and size of the higher parts of th(^ br:iin, l)ut also various details as 

 to the convolutionary pattern. This method has been applied with 

 marked success to the determination of the characters of the lirain 

 in various fossil lemurs by Dr. Forsyth Major and Prof. R. Burck- 

 hardt, and Prof, (xustav Schwalbe has made a large series of such 

 casts from his craniological collection in Strassburg. The interesting 

 observations b}^ Schwalbe" on the arrangement of the " impressiones 

 digitatcV ^ 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 inquir3^ As is 

 well kuowai, the marked prominence at the base of the human skull, 

 separating the anterior from the middle fossa, fits into the deep cleft 

 )>etween the frontal and temporal lobes of the brain, and Schwalbe 

 has shown that this ridge is continued — of course in a much less 

 marked form — along the inner surface of the lateral wafl of the skull, 

 so that a cast of the cranial cavity presents a shallow but easily recog- 

 nized groove corresponding to the portion of the Sylvian fissure of the 

 brain separating the frontal and parietal lobes from the temporal lobe. 

 Further, there is a distinct depression for the lodgment of the inferior 

 frontal convolution, and a cast of the middle cranial fossa shows the 

 three external 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 



'"Uber die Beziehungen zwisohoii Iniienfonn und Aussenform des Schtidels, 

 Deutsches Arctiiv fiir klinische Medicin, 1902. 



