THE NERVOUS SYSTEM 497 



at n, Fig. 148 ; the fore-limb at /./. ; the hind-limb at h.l. ; 

 face at / (see note on Fig. 148) ; tail at t ; eye movement 

 at e.m. ; dilatation of the pupil at p. The movements of 

 flexion, extension, and rotation of the various limbs, head, 

 neck, and trunk, and the more complex movements in the 

 higher animals, have each their separate representative in the 

 cortex. The more complex and delicate the movements, the 

 larger the cortical representation, so that the head and arm 

 areas in the ape and man are more largely represented than the 

 trunk and lower limbs, where the movements are of a simpler 

 character. The thumb area is relatively larger than the shoulder 

 or hip area. In Fig. 150 a lesion is shown of the left hemisphere 

 of the dog, involving most of these centres. The symptoms 

 shown are detailed in the description of the figure. In destruc- 

 tive brain lesions it is observed that the muscles, like those of 

 inspiration, which act bilaterally, are not affected by a uni- 

 lateral lesion. We have previously drawn attention to the 

 fact (p. 150) that the muscles of the larynx have a double 

 representation in the cortex — viz., that both sides are repre- 

 sented in each hemisphere, and the same holds good for the 

 respiratory muscles of the chest and abdomen.* 



The motor area of the cerebral cortex of one of the larger 

 herbivora has recently been investigated by Simpson and King, j- 



These observers have shown that the motor area in the sheep is 

 situated in the superior frontal convolution, and is very limited 

 in extent. This convolution, with the fissures surrounding it, is 

 shown in Fig. 151, while the positions of the motor areas are seen 

 in Fig. 152. The motor area comprises from front to rear centres 

 for (a) face, mouth, and tongue ; \b) head and eyes ; (c) fore-limb ; 

 (d) hind-limb. Of these the fore-limb area is the most, and the face 

 area the least, excitable. The hind and fore limb centres are separated 

 by the splenial sulcus ; stimulation above the sulcus produces 

 flexion and extension of the opposite hind-limb and spreading of 

 the digits. Flexion is always more evident than extension. Stimu- 

 lation below the sulcus produces movements of the opposite fore-limb, 

 flexion in this case also being more frequent than extension. Where 

 the fore and hind limb areas meet, and extending from the splenial 

 to the coronal sulcus (Fig. 151), is an area common to fore and 

 hind limbs, stimulation of which produces movements of the fore 

 and hind limbs of the opposite side, and sometimes of the hind- 

 limb of the same side, but never of the fore. Stimulation of the 

 head and eyes area leads to turning of the head to the opposite side 

 and conjugate deviation of the eyes. The head movement is 



* The two-sided representation in each hemisphere is limited to respira- 

 tion. In other cases each hemisphere causes contraction of chest and 

 abdominal muscles strictly limited to crossed sides, and this is true even 

 of the perineal muscles and sphincter ani (Sherrington). 



■f ' Localisation of the Motor Areas in the Sheep,' Professors Sutherland 

 Simpson and J. L. King, Quarterly Journal of Experimental Physiology, 

 vol. iv., No. 1, 191 1. 



32 



