Summary [CHAP. 



2. Briefly put, it covers the base of the upper and middle frontal gyri, some of the 

 ascending frontal (that not coated by the " precentral " type), a considerable portion of the 

 inferior frontal, including the pars basilaris (area of Broca), the pars triangularis (sometimes), 

 and the pars orbitalis of the frontal operculum. 



3. The calloso-marginal and transverse orbital fissures, at the upper and lower extremities 

 of the area, respectively, form fixed limits, but the anterior boundary is not regularly 

 determined by sulci. 



4. Histologically many of the structural characters noted in the " precentral " cortex are 

 repeated, thus, the general depth is preserved, the difference in regard to nerve fibres chiefly 

 affects the degree of fibre wealth, and save for the giant cells of Betz the cell lamination 

 is remarkably alike. These resemblances suggest a physiological kinship between the two parts. 



5. In the anthropoid ape's brain an " intermediate precentral " area can be defined 

 without any difficulty, but the curious simian disposition of sulci in the lower parts of the 

 frontal lobe accounts for an interesting variation in distribution. Compared with the human 

 brain the orbital extension of the area appears to be dislocated forwards, due to the fact 

 that the " intermediate " cortex insists oil passing forwards to cover the gyrus forming the 

 anterior wall of the fronto-orbital sulcus, at the same time avoiding the field interposed 

 between this sulcus and the apparent insula. At first sight peculiar, this variation is readily 

 explained if we accept the fronto-orbital sulcus of the ape as the equivalent of the human 

 anterior limiting sulcus of the insula, a homology advanced by comparative anatomists and 

 supported by these findings. 



6. Having regard to the discoveries (1) that this cortex bears a structural resemblance 

 as well as a topographic relation to the " precentral " cortex, (2) that the field corresponds 

 in distribution with the area found excitable in the simian brain by experimenters prior 

 to Sherrington and Griinbaum, and (3) that its anterior boundary agrees to a marked extent 

 with the so-called " sensory projection centre " worked out by Flechsig on developmental lines, 

 the proposition is favoured that it participates in the motor function ; and it is submitted 

 that it may represent a higher centre presiding over elements in the " precentral area " 

 proper, in short, that it is designed for the execution of skilled, as opposed to crude and 

 automatic movements. 



7. In the development of this argument the motor components in speech and writing 

 are discussed, as these are acts calling for the exercise of movements skilled in the highest 

 degree and it is most significant that their supposed centres lie within the limits of 

 this field. 



8. Digressing to consider the localisation of the motor speech centre it is submitted 

 that this is probably not so restricted as previously supposed, and that the forward extension 

 of the " intermediate precentral " cortex on the inferior frontal gyrus may have the same 

 function as the cortex of Broca's area. In support of this assumption it is pointed out, in 

 the first place, that histologically the cortex of all this part of the " intermediate precentral " 

 area is alike, that is to say, the area of Broca is not distinguishable by any localised 

 specialisation of structure ; and, secondly, that it is a common matter of clinical experience 

 that a superficial lesion confined to the cortex of Broca's area, is not wholly effective in 

 the production of motor aphasia ; in other words, if the disability is to be permanent the 



