380 



THE BRAIN OF MAMMALS, BY TH. MEYNERT. 



A capsule is thus formed from the convex external surface 

 of the lens-shaped hemispherical vesicle, the lumen of which 

 constitutes the cul de sac of the Sylvian fissure. 



The outgrowth of the bottom of the Sylvian fissure, the island of 

 Eeil, constitutes a measure for the highest grades of development of 

 the brain, because it is dependent upon the size of the lenticular 

 nucleus, which stands in direct relation to the size of the hemispheres. 

 This region of the cortex is connected to a remarkable extent, at the 

 same time, with the power of speech. 



The two to four primary convolutions of the Mammalian brain shape 

 themselves from the fundamentally convex shape of the hemisphere by 

 means of secondary parallel longitudinal grooves. (Leuret, Huschke.) 

 The type of the brain in the Monkey (and in Man) exhibits three 



Fig. 233. 



Fig. 233. Antero-posterior section of the brain of the Cercocebus 

 cinomolgus (slightly enlarged). F, The frontal extremity; 0, occipital 

 extremity ; T, the temporal extremity ; -R, cortex of the cerebrum ; 

 Op, the cortex of the internal lamina of the parietal convolution, with 

 the cortex of the insula bounding the superior fissure of Burdach ; U, 

 the cornu Ammonis ; S H, sulcus hippocampi ; L, the third segment 

 of the lenticular nucleus ; Cl, the claustrum ; A t the nucleus of the 

 amygdala ; Cs, the tail of the corpus striatum ; P, the cushion of the 

 optic thalamus ; G, external corpus geniculatum ; pr, fibrae proprise 

 of two convolutions ; arc, fasciculus arcuatus ; unc, fasciculus unci- 

 natus ; Ig, fasciculus longitudinalis inferior ; Ca, anterior commissure ; 

 in/, inferior cornu of the lateral ventricle ; PI, upper link of the pro- 

 jection system. 



such grooves, though there is a well-marked tendency of the most 

 external one to split into two ; and this type is also characterized by 



