vnj Llinbic Lobe and Olfactory Area 179 



intervening nests are of such small size that it is impossible to make much of their intimate 

 structure, and the only point we need note about them is that they are much more numerous 

 than the large cells. 



The presence of these superficially-placed cell nests has been recognised by several other 

 neuro-histologistSj notably Ramon y Cajal and Hammarberg; the former gives an excellent 

 :n-c(iuni. of the appearances presented by the two varieties of cell when treated by the method 

 of Golgi, and furthermore attaches such functional importance to the area over which the 

 formation is distributed that he distinguishes it by the name " regio olfactiva 1 ." 



Passing on to the next layer we search in vain for the medium-sized pyramidal cells 

 which characterise other regions, and also a layer of giant pyramidal cells is wanting, the 

 place of these two laminae being filled by a deep stratum of cells of approximately equal 

 size, having an average diameter of 20 25 /j, and belonging to neither of the above classes. 

 As seen in Xissl preparations these cells are distinctly pyramidal, with an elongated apical 

 process and two or more short basal dendrites ; the chromophilic elements are not large, at 

 the same time the body plasma accepts the stain fairly readily, and on this account the cells 

 stand out plainly. The nucleus is of ordinary size. Another feature of some importance is 

 that the apical process, as often as not, points obliquely upwards instead of directly towards 

 the surface, and this coupled with their staining reaction makes one think that they are 

 homonymous with cells which one finds at a similar level throughout the gyrus fomicatus. 

 But from Ramon y Cajal's researches it appears that the true morphology of these cells 

 is not revealed until they are impregnated with silver by the method of Golgi, for when so 

 treated it is seen that the basal dendrites break up into an extraordinary number of processes 

 and hang down very much after the manner of a tassel, and judging from Ramon y Cajal's 

 figure the name tassel cell (Quastzellen) seems very appropriate ; another noteworthy feature 

 is that while a few collaterals issue from the apical process, none are to be seen coming 

 from the sides of the cell body, which is distinctly unusual. 



Following on this lamina is a pale strip corresponding in position with the line of 

 Baillarger and almost bare of nerve cells. 



We next come to a layer of large fusiform or triangular cells which are chromophilous 

 and in many respects similar to cells which will be described at length in the prelimbic cortex. 



Beneath this layer and partly mixed up with it are numbers of typical small fusiform 

 cells requiring no special description. 



Distribution of the above-described Type of Cortex. (Plate I.) 



Writers on comparative anatomy have shown us, that in animals with a well-developed 

 sense of smell the anterior end of the gyrus hippocampi swells into a large pear-shaped 

 lobe, which they have designated the lobus pyriformis; and this lobe is separated from the 

 temporal pole by a deep and extensive fissure, which they call the scissura limbica or fissura 

 rhinica. Now I have already alluded to the existence in the human brain of a comparatively 



1 Flechsig has also recognised these cells and regards them as the termini of the fibres of the lateral olfactory 

 root. He further mentions that they agree in structure with the cells of the stratum cellularum pyraruidalium of 

 the cornu ammonia, and indeed are a lateral extension of that lamina. With this statement I was inclined to 

 agree until I read Kamon y Cajal's work, which, with later observations of my own, has convinced me that Flechsig 

 is wrong on both issues (see pp. 176 and 181). 



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