136 Leyton and Slierrinotoii 



tlierefore decided to carry out an inquiry into the motor cortex of the 

 anthropoid apes, more especially from tlie " localisation '" aspect. The 

 followiuiij paper is based on tlie experimental examination of twenty-two 

 chimpanzees, tliree o-orillas, and three orang-utan. The methods employed 

 have included both stimulation and al)lation, but chiefly the former. 



At the time our observ^ations were begun the only recorded experiment 

 on the cerebral cortex of the anthropoid ape was one of stimulation of the 

 cortex of an orang by Beevor and Horsley (1890) (2). The results thej^ 

 arrived at will be referred to later in the present paper ; an excellent 

 diagram sunnaarising them is given by Schafer in his Text-book of 

 Physiology (1900) (37). More recently, observations on localisation in the 

 anthropoid have been (taking them in their successive order of date of 

 publication) two preliminary Notes by ourselves (19); observations on the 

 orang by Roaf and Sherrington (8(i) and by the Vogts (44); on the 

 gibbon by Mott, Schuster, and Sherrington (32): on the chimpanzee by 

 T. Graham Brown and Sherrington (5,6): and on the chimpanzee by 

 T. Graham Brown (8. 4). Individual reference is made to these sub- 

 sen uentlv in the text. 



Methods Employed tn the Present Research. 



For stimulation of the cortex we have used faradisation, applied for the 

 most part by the unipolar method (18, 19). For this a broad copper plate 

 was strapped over a pad wetted with strong sodium chloride solution lying 

 against the sole of the foot contralateral to the hemisphere under examina- 

 tion. The pattern of electrode used was that figured in the Journal of 

 Physiology, vol. xxviii. p. 16 (18). It has the advantage of being easily 

 applied with a light and fairly constant pressure against the cortex surface 

 without risk of pricking the cortex or its pia ; also of being easily steril- 

 ised by the flame, and of being readily bent to any appropriate curve when 

 surfaces not otherwise easily reached have to be explored. The inductorium 

 was of the usual physiological pattern, worked by a single Daniell cell. Tn 

 many instances we used also the bipolar method, the electrode tips being 

 2 mm. apart. Tlie unipolar method is preferable, and gives minuter 

 localisation, especially where, as in certain experiments, a cut surface is 

 to be explored for fibres running at right angles to that surface. 



The animals were in all cases deeply anaesthetised with chloroform and 

 ether mixture for the whole of the operation by which the cortex is exposed. 

 During the actual exploration with faradism the aneesthesia was lightened, 

 since in profound an;esthesia the cortex becomes inexcitable. 



After the dura mater was opened it was always necessary to prick or 

 tear some small holes in the arachnoid to let out the subarachnoid fluid. 

 If that is not done, localisation in the neijjhbourhood of the sulci is almost 

 or quite impracticable. 



A precaution found necessary for success in a prolonged examination of 



