F. Parkes Weber, G. Dorner
1910 The Lancet  
many plausible but mistaken arguments concerning the homologies of sulci. Certain writers have adversely criticised my reference to the cingular sulcus in the carnivora (Fig. 24, as the boundary of the gyrus cinguli, s, on the ground that it is a limiting sulcus of the area striata (Fig. 24, A.s.) ; but in the primitive mammal it may be the limiting sulcus of both-i.e., the line of separation between them. Even when a strip of "association area " develops (as it does in the carnivora,
more » ... n the carnivora, Fig. 25, b) , to separate the two originally coterminous districts, they may still seem to be separated the one from the other merely by a simple furrow, when examined superficially (Fig. 24 ,, because the" association area" (b) and its two limiting sulci (Fig. 25 , l. and ic.) may be quite submerged in a fossa. This case is an admirable illustration, not only of one of the pitfalls to which superficial criticism is liable, but also of the manner in which a simple interterritorial boundary-sulcus may be converted into two limiting furrows, when the two territories become separated by an "association area " (b), which at first may be submerged, though later (Fig. 26 , b) it comes to form part of the actual surface. This brief account of some of the difficulties which complicate the problem of homologising sulci will have made it clear to you that we are still far from a satisfactory interpretation of the configuration of the mammalian neopallium. It will be readily understood that the account of the convolutions of the brain which I wrote for the catalogue of this Museum ten years ago was of a tentative nature, for at that time the complexity of the problems to be solved was not realised : in fact, it was that work which suggested the need for fresh methods of unravelling the complicated network of causal factors, some of which I have laid before you to-day. I have already explained to you how misleading the inferences as to the homologies of sulci may be when based solely upon the evidence of the structure of the cortex, even when the histological survey is quite accurate and beyond reproacha description which can be applied to no published work that I am acquainted with, except the excellent series of memoirs by Dr. K. Brodmann, published in the Journal für Psychologie und Neurologie. But there are certain factors which almost all those who have devoted themselves to the study of histological localisation have ignored : (1) the variability in the relationship of sulci to the neopallial areas, the growth of which is unquestionably the causal agent in their production ; and (2) the rarity of the exact topographical coincidence of a sulcus and the edge of an area to which it is genetically related. If, in a large series of brains, one examines the relationship of a limiting sulcus to the margin of the area which it bounds, it will be discovered that in most cases the distinctive cortical structure does not stop precisely at the bottom of the furrow, but in some instances goes a few millimetres beyond, and in others ceases a few millimetres before, it reaches that point. Yet the evidence afforded by the whole series can leave us in no doubt as to the causal relationship between the sulcus and the edge of the cortical area. The histologist, who laboriously reconstructs the topography of a hemisphere from a multitude of serial sections, usually can find time to examine only one or two examples of a particular species of animal; and, if he finds that a particular area extends slightly beyond, or does not quite reach, a particular sulcus, he is apt to deny the causal relationship between the two, quite forgetful of the fact that the growing cortex is a plastic material, and that the forces which mould it are apt to be applied in a diffuse manner, so that the folding does not take place with that mathematical precision which the histologist seems to expect and demand. ] Thus, for example, even such a careful and painstaking investigator as Brodmann refuses to admit the identity of the s dorsal segment of the sulcus centralis in the lemur's brain (the homology of which has been placed beyond all possi-] bility of doubt bv the researches of Dr. myself) simply because the motor area reaches bevond it to the extent of t one millimetre in a thricemaynified plan 17 If Dr. Brodmann l expects Natnre to work to a degree of accuracy within a 17 K. Brodmann: Beiträge zur histologischen Lokalisation der Grosshirnrinde, Journal für Psychologie und Neurologie, 1908, p. 332 and Fig. 30 range of one-third of a millimetre in the operations of neopallial folding, then he must renounce all idea of homologising any sulci whatsoever. Mr. President, in these three lectures I have done little more than clear from the path some of the obstructions which stand in the way of a fuller comprehension of the mysteries of cerebral architecture ; but if, in doing so, I have called attention to the value and importance of the material in one corner of your Museum I have not laboured in vain.
doi:10.1016/s0140-6736(01)14323-0 fatcat:ujeo75pj55ajzngkvgstbd6emm