ON THE FUNCTIONS OF THE CEREBRAL CORTEX. 
9 
sulcus X. In front and externaily it approaches the arm-area, and excitation along 
the line of junction of the two causes the combined forward movement of the arm 
and lesf which Fee.rier has described."' 
The muscular contractions which are produced by excitation of this strip vary 
according to the place of application of the electrodes, but they are generally such as 
to produce flexion of the joints of the lower limb. Behind the upper end of the 
fissure of Rolando the excitation takes effect chiefly upon the ankle and digits, 
producing most commonly flexion of the foot with either flexion or extension of the 
digits — most commonly the latter (especially near the posterior extremity of the 
area). In front of the upper end of that fissure flexion of the foot and movements 
of the toes are still very common, but the most marked movement is flexion of the 
leg at the knee, caused by strong contraction of the hamstrings, with the addition, 
when the electrodes are applied still more anteriorly, of flexion at the hip, so that 
the whole limb is now brought forward under the abdomen. 
The trunk-area, unlike the last, scarcely, if at all, extends over the margin to reach 
the external surface. We have occasionally obtained movements of the trunk when 
the electrodes have been applied between the sulcus x and the margin, but have 
much more often obtained a negative result as regards the spine and abdominal 
muscles, movements of the leg at the hip and of the arm at the shoulder being 
generally the only effect produced. The movements of the tail, which Ferrier describes 
as being produced by excitations applied over the situation of x, we have not obtained 
at this point. 
Mesults of excitation of the marginal convolution. — As we have already stated in a 
preliminary communication to the Royal Society ,+ electrical excitation of the marginal 
convolution in Monkeys is followed by various movements of the limbs or trunk 
according to the part stimulated. Excitation of this convolution in the prefrontal 
region yields no result. But if the electrodes be applied about opposite the anterior 
end of the corpus callosum, especially close to the margin of the hemisphere, the 
movement of the head and eyes characteristic of excitation of Ferrier's centre (12) 
may be obtained (extension of the head-area, vide antea, p. 8, and Diagram II.). A 
little behind this point well-marked movements of the opposite arm are observed. 
They occur chiefly at the shoulder, and consist usually of retraction of the scapula 
and adduction of the arm to the side, but are frequently combined, especially when 
the electrodes are applied more anteriorly, with movements at the elbow (flexion or 
extension, more commonly the former), and more rarely with extension of the hand. 
This portion of the marginal convolution forms, therefore, an extension over to the 
mesial surface of the hemisphere, of the large arm-area of the external surface [vide 
antea, p. 6). Opposite the level of the anterior extremity of x, contraction of the 
* ' Roj. Soc. Proc.,' vol. 23, 1875. 
■j" HoRSLET and Schafer, "Experimental Researclies in Cerebral Physiology. — I. The Functions of 
the Marginal Convolution," 'Proceedings of the Royal Society,' vol. 36, 1884, p. 437. 
MDCCCLXXXVIII. B. C 
