THE BRAIN. 



427 



FIG. 113. 



result. But at certain circumscribed localities, the application of the 

 galvanic stimulus causes definite movements of the limbs, head, or 

 trunk. These movements always take place on the opposite side 

 of the body. They are different from the general convulsive reactions 

 produced by galvanizing the spinal cord, the trunk of a spinal nerve, 

 or the base of the brain. They 

 are confined to particular muscles 

 or groups of muscles, and produce 

 flexion or extension of the anterior 

 or posterior limb separately, or of 

 a single joint in either. They are 

 not quite instantaneous, but often 

 have a certain appearance of delib- 

 eration, and resemble in character 

 the normal voluntary movements 

 in a waking condition. In the 

 same animal, particular move- 

 ments, such as flexion or ex- 

 tension of the fore or hind paw, 

 always follow galvanization of 

 particular points on the cerebral 

 convolutions, the relation be- 

 tween the spot galvanized and 

 the part moved remaining inva- 

 riable. The spot on the cerebral 

 surface which thus responds to 

 galvanization by the movement of 

 a particular limb or part of a limb 

 is therefore called the "centre of 

 motion " for that part. In differ- 

 ent dogs the special centres of mo- 

 tion are not strictly identical in 

 locality, but they are very nearly 

 so ; and the region within which these centres exist, or the " motor 

 region," is as definitely marked as any other anatomical division of the 

 brain. It comprises chiefly the convolutions surrounding the so-called 

 "frontal fissure," a nearly transverse furrow in the anterior portion 

 of the dog's brain, running outward for a short distance from the great 

 longitudinal fissure. 



It was for some time a matter of doubt whether the localized move- 

 ments in question were produced by stimulation of the cortex, or whether 

 they were due to a diffusion of the galvanic current and consequent irri- 

 tation of more deeply-seated parts, especially the corpora striata. But 

 this doubt is no longer entertained by the majority of physiologists. 

 When the distance between the two electrodes, and therefore the length 

 of the current traversing the convolution, is only one millimetre, galvan- 

 ization of a particular spot may produca, many times in succession, a 



BRAIN OF THE DOG, from above , showing centres 

 of motion in the convolutions. F. Frontal fis- 

 sure. 1. Flexion of head on neck, in the median 

 line. 2. Flexion of head on neck, with rotation 

 toward the side of the stimulus. 3, 4. Flexion 

 and extension of anterior limb. 5, 6. Flexion 

 and extension of posterior limb. 7, 8, 9. Con- 

 traction of orbicularis oculi and other facial 

 muscles. 



