238 Consideration of Function, [CHAP. 



and secondly, the curious way in which the " intermediate precentral " area is pushed 

 upwards by the fronto-orbital sulcus. The distribution of the area on this surface is of 

 further interest because it seems to throw a certain amount of light on the homologies 

 of the part and in particular it explains the sulcus rectus. It will be remembered that 

 in man the anterior border of the field crosses the middle of the sulcus frontalis medius, 

 and now in the ape it similarly bisects the anterior portion of the .sulcus rectus, that 

 portion which in two of my specimens is isolated. Then just as in man part of the postero- 

 inferior boundary is made up of the sides of the angle formed by the sulcus precentralis 

 inferior and the sulcus frontalis secundus, so also in the ape it is the angle between the 

 former fissure and the hinder division of the sulcus rectus which forms the corresponding 

 limit. I think, therefore, that these additional facts of histology add weight to my previously 

 expressed supposition (Chapter on " Intermediate Precentral " Area) that the -posterior and 

 anterior portions of the simian sulcus rectus are the equivalents of the human sulcus frontalis 

 secundus and sulcus frontalis medius respectively. 



B. " Prefrontal " Area. 



The " prefrontal " cortex in the ape is mainly confined to the deep keel-shaped orbital 

 projection of the frontal lobe. Viewed from the mesial surface the anthropoid area looks 

 equal to that in man, but taken altogether its extent is less. 



FUNCTIONS OF THE FRONTAL AND PREFRONTAL AREAS. 



The portions of the frontal lobe which I have just defined comprise a territory the 

 functions of which are but little known, it is a part where theory holds the major hand, 

 one which has proved most resistive to workers in the several departments of experimental 

 physiology and pathology, clinical medicine, embryology, anatomy and histology, both human 

 and comparative, and about which the little knowledge we do possess has only been acquired 

 by negative and roundabout processes of reasoning ; further, as others have rightly observed, 

 it is a realm where localisation, in so much as this applies to the definition of fields 

 having a specific function and a specialised structure, seems unattainable. 



Having always insisted that histological examination of the cortex is to be regarded 

 as an auxiliary force only to be brought into action after a preliminary exploration of the 

 ground has been made by prospectors in other departments, it cannot be expected, now 

 that all other methods of research have proved comparatively unproductive, that microscopic 

 inspection will materially further our knowledge of the function of these parts. Still the 

 modest share taken by the microscope is not to be despised even here. To have obtained 

 a comprehensive view of the cortex investing this region is an advantage, and it is a still 

 further advantage to have reduced the dimensions of the field marked on our map of the 

 frontal lobe as of uncertain function. As we all know not many years ago this field reached 

 as far back as the fissure of Rolando, whereas now we can exclude the greater part of 

 the ascending frontal or precentral gyrus (that covered by the precentral type of cortex), 

 and strong reasons have been advanced for striking out the wider expanse of cortex having 

 " intermediate precentral " characters, so that although we may receive credit for nothing 

 else we have done good in nan-owing the field left for further investigation. But in 

 addition to this the complete survey of the area which I have accomplished sheds a brighter 



