124 Journal of Comparative Neurology. 



in the two classifications is apparent rather than real. There 

 are no hard and fast lines of division corresponding to Ham- 

 marberg's structural regions, but each region shades into the 

 next. In region 3, for instance, the posterior portion, Ham- 

 marberg says, contains larger pyramids and fewer small irreg- 

 ular cells than the anterior. Where the gyrus passes over into 

 the anterior central, there are even a few groups of giant cells. 

 All of these changes of structure in the posterior part indi- 

 cate that it would be as appropriate to class this part of the 

 gyrus as motor, as Flechsig does, as to call it part of the asso- 

 ciation region. 



Region 8, the lower five -sixths of the posterior central 

 gyrus, is classed with the sensory regions, primarily because 

 Flechsig considers it the sensory center for the skin senses, 

 while he regards the anterior central gyrus as the motor center. ^ 

 Moreover the anatomical difference reported by Hammarberg 

 coincides with this view. He finds no giant cells in region 8 

 while the fourth layer is well marked and contains numerous 

 cells. In both these respects the cortex of region 8 differs from 

 the typical motor cortex and approaches the sensory type. 

 Additional evidence for this difference in function between re- 

 gions 7 and 8 is found in the fact that in Hammarberg's patho- 

 logical cases, motor disturbances are uniformly correlated with 

 abnormal structure of the cortex of region 7, but not uniformly 

 with defects in region 8. Beevor and Horsely,^ in their experi- 

 ments on the motor cortex of the monkey, found that electrical 

 stimulation of the cortex of the anterior central gyrus produced 

 movements much more constantly than stimulation of the lower 

 posterior central. All these lines of evidence point to t he fact 

 that the anterior central region is the motor center par excel- 

 lence, and make it seem probable that the posterior central, par- 



M. c. p. 62 ff. Note 29. 



' A Minute Analysis (experimental) of the Various Movements Produced 

 by Stimulating, in the Monkey, different regions of the cortical center for the 

 upper limb, as defined by Professor Ferrier, Phil. Trans. Roy. Soc, London, 

 1887, B. 



