74 8 



THE CEREBRAL CORTEX. 



purpose of operation. 1 The results, as far as they go, conform with 

 those made upon the monkey and orang. 2 Both in the orang and in 

 man a much greater strength of current than that employed for lower 

 animals is needed to provoke movements, a result which appears 

 to indicate that they are caused by excitation, not of the superficial 

 but of more deeply lying parts of the cortex, which is much thicker 

 than in the monkey. The convolutions are also more excitable 

 near their convexity than near the bounding fissures. Both in the 

 orang and in man it is difficult to provoke epilepsy by electrical 

 excitation; and it may be added, it is easier to produce this condi- 

 tion in the dog than in the monkey, and in the rabbit than in the 

 dog. Thus the lower the animal in the scale of intelligence the more 

 easy is it to provoke epilepsy, which is characterised by a condition 

 of abnormal excitability of and spread of excitation over the whole 

 cortex. 



Clinical evidence. — Abundant confirmation is forthcoming regard- 

 ing the situation of the motor areas in man, as the result of clinical 

 observation. On this subject a very large number of cases have 

 been collected and published by Charcot and Pitres, 3 to whose 

 book the reader is referred for the details and diagrams by which 

 the cases are illustrated. They show that the motor zone in man 

 includes only the convolutions adjacent to the fissure of Eolando, 

 namely, the ascending frontal, the ascending parietal, the paracentral 

 lobule, and the Eolandic operculum. 4 Lesions of any of these gyri, 

 even if quite small, always cause permanent paralysis in one or 

 several muscular groups of the opposite side of the body, and 

 are followed by degeneration in the pyramidal tract. The areas 

 are disposed in the following order from above down (Fig. 340, A 

 and B) :— 



That for the lower limb. — In the paracentral lobule and the upper 

 fourth of the two central gyri. The area for the trunk muscles is closely 

 associated with this one. 



That for the tipper limb. — In the middle part of the central gyri, 

 extending from the leg area as far as the sharp downward bend of the 

 fissure of Rolando. 



That for conjugate movements of the eyes and head. — Occupying the 

 ascending frontal gyrus just below the genu of the fissure of Eolando, 

 and extending forwards into the base of the second and third frontal 



gyri- 



That for the face, mouth, tongue, and throat. — In the lower third of 

 the central gyri, and in the Eolandic operculum. 



The motor area in man does not include Broca's convolution, i.e. the 

 base of the third frontal gyrus, lesions of which, although productive of 



1 See the cases quoted by Mills, Brain, London, 1889 ; Beevor and Horsley, Phil. 

 Trans., London, 1890, B, pp. 152-156; and Ferrier, " Croonian Lectures," 1890, p. 34. 

 Cf. also v. Beehterew, Arch. f. Physiol., Leipzig, 1899, S. 543. 



2 Gotch {Brit. Med. Journ., London, 1893, vol. i. p. 1102) got movements of the head 

 (to the same side) on stimulating a point on the nscending frontal gyrus a little below the 

 genu of the bend of the Rolandic fissure. This is also got here in the orang, but not 

 in the macaque. 



3 " Les centres moteurs corticaux chez l'homme," Paris, 1895. 



4 Whether the head and eye movements are represented here only or in a more 

 advanced portion also, as in the anthropoid, does not appear clear as the result of 

 clinical observations ; these movements are rarely if ever wholly lost in cases of cortical 

 paralysis. 



