vir] Liiitfn'c Lobe and Off(t<-fri/ Area 



further researches he seems inclined to reverse the order; relating how in the brain of a 

 foetus 34 cm. long he found the central convolutions quite unmedullated, while some fibres 

 could be made out in the cortex of the unciuate gyrus (lobus pyriformis) and in the anterior 

 perforated spot close to the beginning of the fossa Sylvii. A little further on, however, he 

 states that when inrdullation does begin in the central gyri it proceeds rapidly and soon 

 outstrips that in the olfactory region. In the same paper he indicates how this early develop- 

 ment of cortical olfactory fibres harmonises with previous observations of his own, to the effect 

 that the ganglion cells resident in the lobus pyriformis are the first of all in the human 

 brain to assume a definite form. 



Concerning other parts of the limbic lobe. Flechsig tells us that the fibre development 

 of the cornu ammonis and subiculum follows closely on that of the above-mentioned areas; 

 also that the gyrus fornicatus, especially its middle third, does not come far behind and is 

 to be included among the areas which he has designated primordial. Other points in regard 

 to the gyrus fornicatus which interest me particularly are that the parts numbered 8 and 

 8 a, in Flechsig's older diagrams, approximately correspond with the pregenual field which 

 my observations prove to be the seat of the curious large and deeply-placed chromophilic 

 cells already described; and also that the number 11 is placed over the splenial part of 

 the same gyrus, which I find to be distinguished by a special arrangement of fibres. 



In addition to these observations on the human brain, some carried out by Dollken, 

 Ramdn y Cajal, and others, can be referred to, which, according to Flechsig, substantiate his 

 findings. And, taken all in all, a study of the developing brain strongly emphasises the 

 importance of the lobus pyriformis as an olfactory centre ; it also suggests that other 

 parts of the limbic lobe have a bearing on this function, so harmonising with the findings 

 of histology. 



Histoloyical Evidence. 



At the present day it cannot be said that we lack information concerning the normal 

 histology of the various subdivisions of the limbic lobe, for the work, begun by Arnold, 

 Meynert and Betz, and carried on by Bevan Lewis, Obersteiner, Hammarberg, Kaes, and 

 Kolliker, has been finally rendered so complete by the researches of Calleja and S. Ramt'in y 

 Cajal that there seems practically nothing further to be learnt concerning the actual 

 morphology and arrangement of the cell and fibre elements resident in the cortex of these 

 parts ; not only so, my humble researches, coupled with those of others, have plainly disclosed 

 the territorial distribution of the variations in structure to be met with. 



But much as has been achieved in the direction of histology, the crowning point of our 

 labours, namely, the ability to make a correct and definite statement concerning the part per- 

 formed by the different areas which we have defined, is far removed, information either 

 confirmatory or refutatory which will enable us to form a precise judgment regarding the 

 function of these structures, and help us in the exact cortical localisation of the olfactory 

 and gustatory centres, is sadly wanting. Above all things we seem to lack the knowledge 

 which in the case of some other cortical regions has proved so valuable, I refer to that 

 derived from studies in pathological histology; for instance, we have much to learn of the 

 cortical changes attending uncomplicated atrophy or lesion of the olfactory bulb and 

 peduncle, and have virtually no conception as to what subdivisions such changes would be 

 distributed over. 



c. 25 



