284 Tin' Hoiitoloyies of tlie Poxta ntral Area 



and, to a lesser extent, on the contiguous gyrus marginalis. Now, although Tschermak's figure 

 of the surface distribution of this degeneration is diagrammatic, and also wanting in detail (for 

 instance, he does not indicate the compensatory ansate depression), yet anyone on comparing his 

 plan with mine will be struck by the general resemblance ; thus, in the lower two-thirds of the 

 field (that which Tschennak has cross-hatched, and a part in which I find the structure most 

 typical) we agree absolutely ; only in regard to the upper extent (Tschermak indicates it by 

 vertical lines) do we differ, Tschermak making his field cover more of the marginal gyrus than 

 I do mine. Lastly, Tschermak is emphatic in declaring that no diseased fibres proceed, either to 

 the gyrus fornicatus, or to the gyrus sigmoideus. 



The con-elation of evidence brought out by these totally different and independent methods of 

 research is so remarkable, that even by the greatest sceptic it cannot be regarded as fortuitous. 

 My reasons for believing that, in Man and the man-like ape, the postcentral gyrus is au end- 

 station for impressions of common sensation, have been set forth at length already, but I may 

 here repeat that one of my grounds for that assumption was the widely different nature of the 

 cortex covering the same gyrus. Summed up, therefore, the position is as follows : utilising one's 

 knowledge of the histology of the Primate cortex, one has found that an area, bearing similar 

 architectural characters, can be mapped out in the brains of three members of different lower 

 animal families ; not only so, the area, in the case of the cat, agrees very closely with the field 

 to which Tschermak traced secondary degeneration, after experimental interruption of the sensory 

 tract in the same animal. 



The evidence on this point would be perfect were it not that a discordant note is struck by the 

 embryologist. From what we know of the sequence of maturation of different groups, or tracts, 

 of medullated nerve fibres, we would expect that those pertaining to this particular area, being 

 sensory, would show their myeliu at an earlier date than those of surrounding parts, especially 

 than those of the motor area, and yet the researches of Professor and Madame Vogt, on the 

 brain of the puppy and kitten, give meagre support to our anticipation. They only tell us that 

 the earliest and richest myelimsation occurs in the gyrus coronalis and in the postcrucial gyrus, 

 while the anterior cruciate limb, the oral part of the gyrus marginalis and the remaining com- 

 ponents of their " regio precox anterior '' do not show so many fibres at the same period. I also 

 observe, in Dollken's maturation table, that although the cortex of the gyrus coronalis is placed first, 

 it is bracketed with the crucial cortex. 



This discrepancy in the evidence is of course worthy of serious consideration, but it does not 

 as yet overthrow our view. Those of us who have undertaken the task of following variations 

 in structure from section to section, in successive series, are mindful of the extreme caution we 

 had to exercise in the avoidance of error, and this was particularly the case when we had to 

 deal with a field of cortex about which preconceived ideas had taken firm root, such as that 

 surrounding the fissure of Rolando or its homologue ; and I may remind the reader that the 

 particular area in the cat we are discussing did not definitely reveal itself to me until I had 

 cross-examined sections stained for nerve cells. Therefore I think it possible, that if the embryo- 

 logists named will reexamine their sections in the light of what has been set forth in more 

 recent publications they may be induced to alter their cerebral maps. 



Apart from this, it appears that the rules governing maturation of nerve fibres do not apply so 

 rigidly to those resident in the cortex as in the spinal cord ; or, perhaps it is more correct to say, 

 that the sequential variations in myelinisation of different tracts of fibres, in particular the 

 variation between motor and sensory developments, are more difficult to determine by cortical than 

 by spinal examination. For instance, we know that in the spinal cord of the newly-born cat and 

 dog the sensory tracts are already developed while the myelinisation of the motor tracts is still 

 imperfect, and yet the Vogts and Dollken all tell us that not a single medullated fibre of 



