MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 



359 



Distance from cc to po 



" " po to ca 



Length of Sylvian fissure 



" " central " 



" " ext. perpendicular fissure 



" " 1st temp 



Distance from upper extremity of Sylvian to lower 



extremity of central 



Distance from upper extremity of Sylvian to upper 



extremity of cc 



Length of interparietal 



Angle of cc with fissura longitudinalis 



Macacus 

 iiemestrinus. 



Macacus 

 iiemestrinus. 



H 

 2i 



60° 



li 

 li 



2i 



17 

 li 

 60° 



Macacus 

 cynomolgus. 



TB" 



7 

 ¥ 



60° 



Cercopithecus 

 callitrichus. 



T"S" 



li 



15 



T? 



1 



111 



L T5 



60° 



The above measurements would seem to indicate that the primary fissures are 

 not as variable, at least in the monkeys, as many have supposed, and furnishes 

 additional evidence that the fissures are the result of determinate laws of growth. 

 I have recently been accumulating observations on convolutional measurements 

 made on the brain immediately after removal, but as yet these are not extended 

 enough to enable proper comparisons to be made. Complete triangulation of the 

 brain surface and careful measurement of the depths of the various fissures, both 

 in the adult and embryonic stages, of different animals will undoubtedly lead to 

 valuable results, not only as regards general morphology, but also in anthropology 

 and medicine. Such careful and elaborate work will, however, require months or 

 years for its thorough and satisfactory accomplishment. A few facts of this kind, 

 as regards the depth of the fissures, have been supplied by Jensen. 1 



The following facts seem to be indicated by a careful study of the fissures of 

 the cerebral surface. The fissura Sylvii unlike all the other fissures of the hemi- 

 sphere represents an area of retarded or slow cerebral growth, as represented in its 

 earlier stages by the fovea centralis ; whilst the insula is produced by a localized 

 swelling or growth taking place upon its surface. It is finally converted into a 

 fissure by the over-growth of the occipitofrontal and temporal lobes, due to their 

 enlargement within a confined space. The great longitudinnl fissure in the same 

 way is produced by the flattening of the two mesial surfaces of the prosencephala, 

 due also to confined growth. 



With the appearance of the primary radiating furrows we have indications of 

 direct inrollings into the cavity of the ventricles, due to pressure forces produced by 

 the more slowly expanding skull. In the same manner the primary and funda- 

 mental furrows of the mesial surface, the mesial arched and the calcarine are due to 



1 Uutersuchungen iiber die Beziehungen zwischen Grosshiru und Geistesstorung an sechs Gehirnen 

 geisteskrauken Iudividueu. Psych. Arch, v., 1874-75. 

 45 JOUEN. A. N. S. PHTLA., VOL. X. 



