248 Summary [CHAP. 



" intermediate precentral " in the almost complete absence of fibres of large calibre both 

 in the projection and association systems ; it, however, contains elements of medium size. The 

 change in cell lamination which I have mostly relied upon in distinguishing the " frontal " 

 from the " intermediate precentral " cortex affects the external and internal layers of large 

 pyramidal cells ; in the first-named cortex a reduction in size and number of these elements 

 is apparent. 



4. The " prefrontal " area is less extensive than the " frontal," it comprises the pregenual 

 portion of the marginal gyrus, on the mesial surface ; the anterior end of the second frontal 

 gyrus, on the outer surface ; and all the orbital surface in front of the sulcus orbitalis trans- 

 versus and within the external sagittal. 



5. The structural development of the " prefrontal " cortex is exceedingly low. It presents 

 an extreme of fibre poverty ; all its fibre elements are of delicate calibre, and its association 

 system is particularly deficient. Its cell representation is on a similar scale. The cortex 

 is also shallow. 



6. " Frontal " and " prefrontal " areas are as readily defined in the anthropoid ape as 

 in the human being. But man has a decided advantage over the ape in regard to the 

 development and extent of the " frontal " area. In the case of the " prefrontal " area the 

 disparity is less marked. 



7. Without adding materially to our knowledge of the functions of the frontal lobes 

 histology throws light on some of the observations of previous writers. 



8. The prefrontal region is absolutely silent under the influence of faradic excitation, 

 and this is probably accounted for by its poor structural representation. 



9. No explanation of the truth that stimulation of the frontal lobe produces eye move- 

 ments can be -given, but the area active in this respect lies within the "frontal" field, and 

 the field has its analogy in the human brain. 



10. There is a conflict of evidence on the effect upon intellectual processes of ob- 

 literation of the frontal lobe ; it is suggested that Bianchi, Ferrier and others obtained 

 positive results because their area of destruction embraced the " frontal " as well as the 

 " prefrontal " area ; and Horsley and Schafer negative results because they ablated the 

 " prefrontal " area alone. 



11. As Welt showed, gross lesions of the frontal lobe give rise to curious changes in 

 character, but our knowledge of the psychic functions of the frontal lobe in the human 

 subject is very imperfect. 



12. On analysing Flechsig's results obtained from myelogenic research, the maps of the 

 cortex he has drawn do not differ essentially from mine. The " prefrontal " cortex appears 

 to be the last to become medullated. 



13. Maintaining on physical grounds that cortex built up on a weak framework of nerve 

 fibres, e.g. the " prefrontal " and " frontal," will be the first to show macroscopic change in 

 the course of cerebral wasting, and the contrary, and holding that serious microscopic changes 

 which may be present in stoutly built cortex, e.g. the " precentral," are likely to be overlooked 

 because gyri so covered preserve their outward form, I am of opinion that we must for the 

 present refuse to accept Bolton and Schaffer's conclusions concerning the frontal atrophy 

 seen in different forms of dementia, notably that of general paralysis, as evidence either 



