6o8 



MOTOR CENTRES IN TH MARGINAL CONVOLUTION. 



ascending parietal and frontal convolutions below the arm-area, down to the fissure 

 of Sylvius, and including the external surface of the operculum.] 



[The head-area, or area for visual direction, comprises part of the frontal lobe 

 from the margin of the hemisphere to the face-area. In front it is bounded by the 

 non-excitable part of the frontal lobe. Its stimulation gives the results obtained 

 by Ferrier on stimulating his No. 12 centre. The leg-area is partly situate on 

 the mesial surface, but it extends over to the external surface from the parieto- 

 occipital fissure nearly to the level of the anterior end of the small sulcus marked 

 s. The trunk-area scarcely extends over the margin to reach the external 



[Schafer and Horsley have extended Ferrier's researches, and shown that motor 

 centres exist in the marginal convolution (fig. 486), which is excitable only in 

 that portion corresponding in extent (antero-posteriorly) to the excitable portion 



Fig. 485. Fig. 486. 



Fig. 485. Diagram of the motor areas on the outer surface of a monkey's brain {Horsley and 

 Seh&fer). Fig. 486. Diagram of the motor areas on the marginal convolution of a 

 monkey's brsiU\[(HorsIcy aiid ScM/er). 



of the outer surface of the hemisphere. Anteriorly it reaches forward to a line 

 which is opposite the junction of the posterior and middle thirds of the superior 

 frontal convolution (centre 12), while posteriorly it extends backwards opposite to 

 the parietal lobule, including the paracentral lobule, which contains large multipolar 

 pyramidal motor cells. The rest of the mesial surface is excitable. They find that 

 the centres are arranged from before backwards in the following order : (1) 

 Movements of the head this area is very small, and belongs to the large head- 

 area on the external surface ; (2) of the fore-arm and hand ; (3) of the arm at the 

 shoulder ; (4) of the upper dorsal part of the trunk ; (6) of the leg at the hip ; (7) 

 of the lower leg at the knee ; (8) of the foot and toes.] 



Excitation of the Area AS produces movements of the arm (fig. 489). These vary according 

 to the spot stimulated, but towards the anterior part of the area, movements of the wrist and 

 fore-arm, towards the posterior part movements of the arm and shoulder, are more frequently 

 the result of the excitation. Excitation of Tr produces movements of the trunk, generally 

 arching and rotation. Those movements which are called forth by stimulating the anterior 

 part of the area are usually confined to the upper part of the trunk (thoracic region), and are 

 often associated with movements of the shoulder and arm ; those called forth by stimulating 

 >terior part are movements of the abdominal and pelvic regions and of the tail, and are 

 often associated with movements of the hip and leg. Excitation of the area L produces move- 

 ments in the lower limb. These vary according to the part stimulated, extension of the hip 

 being especially associated with excitation of the anterior part of the area, and contraction of 

 the hamstrings with excitation of the middle part.] 



[Do similar Centres exist in Man ? The results of clinical and pathological 

 investigations show, that similar although not absolutely identical areas exist in 

 man. The motor areas, or those which have a special relation to voluntary motion 



