The Excitable Cortex of the Chimpanzee, Orang-Utan, and Gorilla 183 



May 5. — Same condition. 



May 10. — Right shoulder seems to be fully used now ; the second 

 operation had seemed to impair its movement to some extent. Hand, etc., 

 used freely, and seem to have been in nowise impaired by second operation : 

 they seem in the .same condition as recorded in the note written on 

 April 26, certainly no worse. 



May 14. — Animal well. Wound is practically healed. Animal deeply 

 narcotised with chloroform ; whole centralis region of left hemisphere 

 exposed, faradi.sed point for point, mapped, and results recorded. Results 

 of stimulating cortex adjoining borders of lesion .same as Ijefore. Lesion 

 measured 10 mm. along lower horizontal border, 13 mm. along upper 

 horizontal border, and has a vertical length of 14 mm. While the animal 

 was being put under the anse-sthetic it was noticed that it clenched its 

 right hand vigorously on several occasions, exerting considerable force with 

 fingers and thumb. 



Left hemisphere's centralis region then exposed and explored. Animal 

 then killed with chloroform. 



Bulb and cord examined by Marclii method revealed a heavy degenera- 

 tion in the left pyramidal tract (fig. 20). In the pyramids the degeneration 

 was entirely confined to the left pyramid. At the region of the most 

 anterior part of the pyramidal decussation some of the degenerated fibres 

 are seen to be among the very first to decussate (fig. 20). In the left 

 pyramid the degenerated fibres, although scattered over the whole cross 

 area of the pyramid, were somewhat less numerous, in comparison wdth 

 normal fibres, at the ventral lateral angle than elsewhere. In regions of 

 the decussation, where the decussation is in full progress and the degenerat- 

 ins: fibres are undera;oin2: that re-arrangement in large bulk, it can be 

 clearly seen that a certain few of them pass slanting dorsally and toward 

 the left into the dorsal part of the lateral column of the ipsilateral side 

 (34, 41, 25), although the vast majority cross to the lateral column of 

 contralateral side. In the upper cervical region (fig. 20) the degeneration 

 consists of a heavy crossed pyramidal field, occupying most of the contra- 

 lateral lateral column except for a well-marked border zone and for a 

 ventral area. In the 2nd and 3rd cervical levels a few degenerated fibres 

 lie at the extreme edge of lateral column for a short strip about midway 

 between the dorsal and ventral roots. Many degenerated fibres lie in the 

 reticular formation at the base of the dorsal grey horn. In the ipsilateral 

 half of the cord there exists a slight and scattered degeneration in lateral 

 column, occupying about the same area as that of the crossed pyramidal of 

 the contralateral side (16, 40, 41, 25). In the ipsilateral ventral column 

 there is a well-marked ventral pyramidal tract (19, 42) degeneration 

 bordering the whole length of the cross-section of the lip of the ventral 

 fissure (figs. 20, 21). 



In lower cervical reo-ion the crossed and uncrossed lateral column 

 degenerations have become very distinctly less heavy, although their areas 



