594 PHYSIOLOGY CHAP. 



direct relation with the sensory endings, but lie chiefly in the 

 paracentral lobule, the precentral gyrus, the introflexed cortex of 

 the Rolandic sulcus (fissure), and the posterior segment of the first 

 frontal convolution. According to Flechsig's later conclusions 

 (1904), the sensory-motor zone, properly so-called, lies only within 

 the Eolaudic fissure ; the convexity of the precentral convolution 

 is almost purely motor, and the convexity of the post-central 

 convolution is almost purely sensory. This also agrees with the 

 fact that the giant pyramidal cells are very few in the cortex of 

 the post-central convolution (Brodmann). But Flechsig's diagram 

 seems to us incorrect, as it makes the boundary between the 

 mixed zone and the sensory and motor zones, and between these 

 and the inexcitable frontal and parietal limiting zones, too sharp 

 and distinct. 



X. The functions of the sensory -motor area of the cerebral 

 cortex are intimately connected with those of the sub-cortical grey 

 nuclei which are situated toward the base of the cerebral hemi- 

 sphere, the principal being the so-called corpora striata, i.e. the 

 caudate and lenticular nuclei. As shown by Fig. 263 (p. 530), the 

 caudate nucleus is the medial, intra-ventricular portion, the 

 lenticular the lateral extra- ventricular part of the corpus striatum. 

 The two nuclei are separated from each other by a layer of white 

 fibres the so-called internal capsule which are continuous with 

 the fibres of the white matter of the hemispheres and spread out 

 like a fan in the direction of the cortex (corona radiata of Eeil). 

 The two nuclei, however, are not completely separated, as there 

 are a number of small bridges of grey matter, particularly in the 

 anterior limb of the capsule, which unite them. 



From the phylogenetic and ontogenetic point of view the basal 

 ganglion or corpus striatum precedes the formation of the mantle 

 or pallium, and constitutes the base of the telencephalon or fore- 

 brain, which develops from the first secondary vesicle. From this 

 fact it may be concluded with probability that the functions of the 

 two principal nuclei of the corpus striatum in mammals and man 

 do not differ essentially from, and are of the same order as, those 

 of the cerebral cortex. 



A number of clinical and anatomo-pathological observations on 

 man have proved that an apoplexy which injures the fibres of the 

 middle third of the internal capsule produces sensory and motor 

 hemiplegia on the opposite side of the body, showing that the 

 fibres of this segment of the capsule are in connection with the 

 sensory-motor area of the cortex. On the other hand, experiments 

 on animals have shown that total extirpation of this area pro- 

 duces degeneration of the whole of the pyramidal tract in the 

 middle third of the capsule. Lastly, it is proved by anatomy and 

 experiment that the fibres of the anterior segment of the capsule 

 are in connection w T ith the prefrontal region of the pallium, 



