GENERAL PHYSIOLOGY OF THE CEREBRUM. 201 



muscular) extend forward into the cortex of the frontal lobe is 

 not clearly shown by experimental or clinical evidence. Flechsig, 

 from his studies upon the time of myelinization of the afferent 

 fibers in the embryo brain, concludes that this is the case, and 

 that, therefore, the motor and sensory areas overlap for a part 

 at least of their extent (see p. 226 and Fig. 98). On the con- 

 trary, in an interesting report by Gushing* of two cases in which 

 the anterior central convolution was stimulated in conscious 

 patients, it is stated that there was no sensation other than that 

 arising from the change in position of the muscles which were 

 thrown into contraction. In the motor area there are numerous 

 connections by association tracts with other parts of the brain. 

 By this means the motor area, without doubt, is brought into 

 relation with many other parts of the cortex, and the sensations 

 or perceptions aroused elsewhere may react upon the motor paths. 

 A voluntary movement, however simple it may be, is a psychologi- 

 cal act of some complexity, that is to say, every movement is pre- 

 ceded or accompanied by certain sensations and perceptions which 

 depend upon sensory stimulations occurring at that time, or upon 

 experiences derived from conditions of excitation that have 

 occurred at some previous period every action is part of a 

 train of conscious or subconscious processes whose neural mech- 

 anism extends over wide regions of the cortex. The mental 

 processes, the associations that lead to and originate the motor 

 discharge, the mental image of the movement to be effected, 

 cannot be definitely located in the cortex, and it is possible that 

 the so-called motor area itself participates in these psychical ante- 

 cedents. But what may be said with confidence is that the im- 

 mediate origin of the outgoing motor impulse lies in the area along 

 the anterior margin of the central sulcus of Rolando, which con- 

 tains the foci, so to speak, into which all accessory processes are 

 gathered, so far as they affect our muscular acts, and from which 

 emerge the actual efferent stimuli to the different muscles. 



* Gushing, "American Journal of Physiology " 1909 ("Proc. Amer. 

 Physiol. Soc."). 



