1046 MOVEMENTS OF CORTICAL ORIGIN. [BOOK m. 



and on that other side alone. Thus when the area for the fore 

 limb is stimulated on the left hemisphere it is the right fore limb 

 which is moved. This is in accordance with what we have learnt 

 of the pyramidal tract and its ultimate entire decussation before it 

 reaches the motor nerves, the decussation either occurring mas- 

 sively as in the case of the crossed pyramidal tract, or in a more 

 scattered manner along the upper part of the spinal cord in the 

 case of the direct pyramidal tract ; and, as we have seen, there is 

 a similar decussation for such part of the pyramidal tract as is 

 connected with the cranial nerves above the decussation of the 

 pyramids. Except in the case of certain areas for movements 

 naturally bilateral of which we shall speak presently, the move- 

 ment is normally on the crossed side, and on the crossed side only. 

 Under abnormal conditions however the limb of the other side, 

 that is of the same side as the hemisphere stimulated, may move 

 also. But such an abnormal movement of the same side has not 

 the same characters as the proper movement of the crossed limb. 

 Instead of being an orderly coordinate movement, it is a more 

 simple, either tetanic or perhaps tonic, or rhythmic, clonic, con- 

 traction of the muscles. Obviously its mechanism is of a different 

 nature from that by which the proper movement of the crossed 

 limb is effected ; but it is important to bear in mind that a move- 

 ment of the uncrossed limb may take place ; and further that, the 

 abnormal conditions continuing, similar movements of an uncoor- 

 dinated character may spread to the hind limb and other parts of 

 the crossed side, though the stimulation be still confined to the 

 arm area, then to other parts of the uncrossed side, until as we 

 have said the whole body is thrown into epileptiform convulsions. 

 This feature must not be forgotten. In fact it may be fairly 

 insisted upon that while we may speak of a particular coordinate 

 movement as being the normal outcome of an ordinary careful 

 stimulation of a particular area in a normal condition, it is no less 

 true that diffuse uncoordinated movements, culminating in general 

 epileptiform convulsions, are the natural outcome of the stimula- 

 tion of any area in an abnormal condition. And in attempting to 

 form any opinion of the nature of the first act, we must bear the 

 second in mind. 



As we said above, the movements resulting from cortical 

 stimulation are most conveniently described in terms of parts of 

 the body, of the arm, of the thumb, of the tongue, &c. The 

 movements of the same part may be further distinguished by 

 means of the nomenclature usually adopted in speaking of mus- 

 cular movements, such as flexion, extension, abduction, adduction, 

 &c. ; so that, within the area bearing the name of some particular 

 part, such as the wrist for instance, we have to distinguish an area 

 for the flexion, and another for the extension of that joint ; and in 

 like manner in reference to other parts. But it will be readily 

 understood that it is easier to map out the area for a particular 



