The Excitable Cortex of the Chimpanzee, Orang-Utan, and fJt^rilla 175 



fissure when that is present. Over the area one or more large veins 

 coniiMonly traverse the face of the convolution (fig. IS), rendering the 

 experimental examination of the area somewhat difficult. From the 

 abdominal wall area anal movement is sometimes elicitable secondary to 

 movements of the abdominal wall. 



5. Lejj Area. 



Leg Area. — The movements of the several parts of the limb seem more 

 commingled in this area than are those of the separate limb parts in the 



^>(vjkA\ 



^vV / 



',J\x\Wc 



.^' 



>A<« 



\oi 



"i. 





Fig. 18. —The veins passing over trunk area of motor cortex in a large chimpanzee ; 

 drawn by Professor Harvey Gushing. 



arm area. Nevertheless a general sequence of foci of main representation 

 is recognisable ; as the area is examined from below upwards this sequence 

 runs hip, knee, ankle, and digits. The leg area extends over the mesial 

 border of the hemisphere, and dips into the mesial surface for about one- 

 third of the depth toward corpus callosum (figs. 2, 7 B, 9, 10, 13, 14, 15, 17, 

 24). The area does not usually follow sulcus centralis to the extreme end 

 of the sulcus, but leaves it a few millimeti-es below that, and slants obliquely 

 forward over the mesial edge of the hemisphere. 



Hip. — The movements have a wide focal field; in our experience, the 

 lowest situate of the movements is flexion. On the whole, extension of hip 

 lies farther anterior than does flexion. In some specimens, notably in one 

 orang, extension of hip was represented as a primary movement over a 

 much wider field than was flexion, but the reverse is more usual. 



VOL. XL, NO. 2. — 1917. 12 



