TOPOGRAPHY OF THE MOTOR CENTRES. 



707 



middle three-fifths of the ascending parietal convolutions, while the leg centre lies 

 at the upper end of the sulcus and extends backwards into the parietal lobule (and 

 perhaps on to the superior frontal convolution) (fig. 488). The leg centre is con- 

 tinued over on to the paracentral lobule, opposite the upper end of the fissure of 

 Rolando, in the marginal convolution on the mesial aspect of the hemisphere (fig. 

 490), where the centres for the muscles of the trunk also exist (p. 698). The centre 

 for speech is in the posterior part of the third left frontal convolution (fig. 488). 



Blood Supply. These convolutions are supplied with blood from 4 to 5 branches of the 

 Sylvian artery, which may sometimes be plugged with an embolon. When a clot lodges in 

 this artery, the branches to the basal ganglia may remain pervious, whilst the cortical branches 

 may be plugged (Duret, Heubner) ( 381). 



[Hemiplegia consists of motor paralysis of one-half of the body, although, as a 

 rule, all the muscles are not paralysed to the same extent ; in some there may be 

 complete paralysis, i.e., they are entirely removed from voluntary control, while in 

 others, there is merely impaired voluntary control. It may be caused by affections 

 of the cortical areas or by lesion of the motor tracts above the medulla, and the 



paralysis is always on the side 

 opposite to the lesion, owing to 

 the decussation of the motor paths 

 in the medulla. If the case be a 

 severe one, we have what Charcot 

 terms hemiplcgie centrale vulgaire, 

 or "complete hemiplegia," due to 

 lesion of the cortical centres for 

 the face, arm, and leg. While the 

 arm and leg are completely para- 

 lysed, the lower part of the face is 



Fig. 490. Fig. 491. 



Fig. 490. Transverse section of a cerebral hemisphere. CCa, corpus callosum ; NC, caudate 

 nucleus ; NL, lenticular nucleus ; IC, internal capsule ; CA, internal carotid artery; aSL, 

 lenticulo- striate artery ; (" Artery of haemorrhage ") ; F, A, L, T, position of motor areas 

 governing the movements of the face, arm, leg, and trunk muscles of the opposite side 

 {Horsley). Fig. 491. Scheme of the innervation of bilaterally associated muscles {Ross). 



more affected than the upper half, which is usually not much affected. All those 

 movements under voluntary control, and especially those that have been learned, 

 are abolished, whilst the associated and bilateral movements, which even animals 

 can execute immediately after birth, remain more or less unaffected. Hence, the 

 hand is more paralysed than the arm ; this, again, than the leg ; the lower facial 

 branches more than the upper ; the nerves of the trunk scarcely at all (Ferrier). 

 When an extraordinary effort is madej it will be found that there is some impair- 

 ment of the power of the muscles of mastication and respiration, although the 

 muscles on opposite sides act together (Gowers). The trunk-muscles, as a rule, are 



