The Cerebrum. 421 



mesial surface of the parietal lobe, i.e., the prsecuneus, 

 whereas, between the parieto-occipital fissure and the cal- 

 carine fissure, is the inner surface of the occipital lobe, 

 viz., the cuneus, and, lastly, beneath the calcarine fissure 

 is the posterior part of the lingual lobe. On drawing the 

 anterior end of the tempero-sphenoidal lobe backwards, 

 and the frontal lobe forwards, and then, on raising up the 

 lower conjoined ends of the ascending frontal and the as- 

 cending parietal convolutions, the island of Reil is ex- 

 posed, having been hidden by these conjoined ends, which 

 are, on that account, called the operculum. 



The cerebellum, situated beneath the tentorium cere- 

 belli, is composed of two lateral lobes united by the vermi- 

 form process. 



Cerebral Localization. Motor centres. Experi- 

 mental research and pathological conditions have 

 shown that the centres which preside over motion 

 are situated in the neighborhood of the fissure of 

 Rolando. In general terms, this region may be 

 divided into fifths the upper fifth presiding over 

 the leg; the middle two-fifths, over the arm, and 

 the lower two-fifths over the face, speech, etc. The rela- 

 tive position of the leg centres, from above downwards, 

 is as follows, viz., great toe, outer toes, ankle, knee and 

 hip. For the arm centres, the order from above down- 

 wards is shoulder, elbow, wrist, fingers, thumb; while, 

 for the face, in the same order, are, elevation and depres- 

 sion of the angles of the mouth, lips, tongue, throat. In 

 front of these centres is that for the larynx, and for speech, 

 the latter centre, being situated in the posterior portion of 

 the third frontal, or Broca's convolution. (Fig. 11.) 



Sensation. Some experimenters place the cerebral 

 centres for sensation in the neighborhood of the motor 

 area of the cortex, but the weight of investigation is 



