282 SCIENCE PROGRESS. 



a point of cerebral cortex connected with movement of one 

 of the fore-paws. The strength of stimulus chosen is one 

 just insufficient to evoke the movement. By stroking 

 gently the skin of the paw itself the inefficient excitation is 

 made at once efficient. Again ; cortical excitation eliciting 

 from the limb muscles a contraction of definite latency, this 

 latency is increased two or three-fold by simultaneous excita- 

 tion of sensory fibres from the limb itself. These easily- 

 affected centres in the parietal cortex are, so to say, threaded 

 upon extensions of the neuro-muscular circuits of Charles 

 Bell (or the diastaltic arcs of Marshall Hall). The remark- 

 able extent of spatial differentiation of these extensions of 

 the circuits was early demonstrated by Ferrier (1873). The 

 connection of the cortex with the neuro-muscular circuits 

 even with the skeletal is however far from being equal for 

 them all. Munk has insisted on three main grades of tie to 

 be distinguished. Between the cortex and some of the 

 circuits he doubts the existence of anv tie at all. On the 

 other hand, Hughlings Jackson has argued for connection 

 between cortex and each and every circuit — of course 

 not equal intimacy of connection. The movements 

 damaged most by destruction of the cortex cerebri are 

 movements fine in kind, such as those performed by 

 the fingers and the thumb. Of such movements some 

 are after extensive injury to the gefuhl-sph'dre never 

 again executed. But coarser movements such as those 

 at hip and shoulder suffer a slight derangement which is 

 temporary. 



Munk suggests that this difference is due to the finer 

 movements being worked through cortical centres acting 

 across subcortical, the latter of themselves sufficient for 

 coarser co-ordinations such as those at the shoulder, etc. 

 Against this suggestion is the known directness of tie 

 between the cortical cells and the segmental spinal centres 

 via pyramidal tract. The cortical centres are no doubt 

 connected with countless cerebral subcortical, but yet we 

 must think that in the execution of fine movements the 

 former supervise the centres of lowest level directly, not 

 indirectly. In estimating degree of impairment of move- 



