THE BRAIN. 



495 



this condition is due to a defect in the internal ear, there is an 

 absence of the dizziness experienced by normal individuals when 

 rapidly rotated in a swing. The vertigo of Meniere's disease is 

 accompanied by changes in the internal ear. It has also been 

 observed that defects of locomotion and equilibration are more 

 common in deaf and dumb children than in those that are normal. 

 Static Equilibrium. By this term is meant the equilibrium of 

 rest, and Lee regards the utricle and saccule as being the organs 

 concerned in this function. That is, that the knowledge of the 

 position of the head while at rest is communicated to the co-ordi- 

 nating center in the cerebellum by the pressure of the endo- 



F 



FIG. 286. View of the brain from above : A, anterior central or ascending 

 frontal convolution ; B, posterior central or ascending parietal convolution ; C, cen- 

 tral fissure, or fissure of Rolando ; cm, callosomarginal sulcus ; F, frontal lobe ; Fi, 

 upper, F-2, middle, FA, lower frontal convolution ; /i, superior frontal sulcus ; /2, 

 inferior frontal sulcus ; fa, vertical fissure (sulcus prsecentralis) ; ip, interparietal 

 sulcus ; 0, occipital lobe ; o, sulcus occipitalis transversus ; Oi, first occipital convo- 

 lution ; 02, second occipital convolution ; P, parietal lobe ; po, parieto-occipital 

 fissure ; Pi, upper or posteroparietal lobule ; Pz, lower parietal lobule, constituted 

 by ^2, gyrus supramarginalis ; P/, gyrus angularis; S\, end of tbe horizontal branch 

 of the fissura Sylvii ; ti, upper temporal fissure. 



lymph upon the otoliths, and these in turn upon the hair-cells of 

 the maculae acusticae. 



Dynamic Equilibrium. This is the equilibrium of motion, and, 

 as already stated, is presided over by the semicircular canals, 

 from which impressions pass to the cerebellum. 



The Cerebrum. The cerebrum, which in man makes up 

 about four-fifths of the encephalon, is divided into two hemi- 

 spheres which are separated by the great longitudinal fissure (Figs. 

 286-289), but are connected by a white commissure, the corpus 



