VARATIONS IN FISSURES AND CONVOLUTIONS OF BRAIN. i6l 



especially to the hippocampal convolution, which in many smooth-brained osmatic 

 mammals forms a considerable proportion of the hemisphere (lobus hippocampi). 



The term rhinencephalon is limited by Turner to the olfactory and hippocampal lobes, but 

 there seems no sufficient reason for excluding the remainder of the limbic lobe, the several parts 

 of which are all closely inter-related. At the same time it must be pointed out that the 

 limbic lobe unquestionably subserves other functions beside that of a central organ for the 

 olfactory sense, since it is present even in those mammals (Delphinidse) which are devoid of 

 an olfactory sense, and in which the olfactory lobe proper is entirely absent. The results of 

 experiment seem to indicate an association of parts of the limbic lobe with the perception of 

 tactile sensations. (Consult on the comparative development of the rhinencephalon and the 

 mantle in mammals, " The Convolutions of the Brain, a Study in Comparative Anatomy," 

 by Professor Sir W. Turner, Journal of Anatomy, October, 1890.) 



ON THE VARIATIONS WHICH OCCUR IN THE DISPOSITION OP THE FISSURES AND 

 CONVOLUTIONS IN INDIVIDUALS OF DIFFERENT AGE, SEX, INTELLECTUAL 

 DEVELOPMENT, AND RACE. 



Very considerable variations are found in the course and relative development of the 

 fissures and convolutions, "and this not only in different individuals, but also on opposite sides 

 of the same brain. Even the principal fissures, under which term may be included both those 

 which occur as complete folds of the hemisphere-wall (Sylvian, hippocampal, calcarine, 

 parie to-occipital, and collateral), and those which are the first to make their appearance (about 

 the sixth month of fcetal life) as indentations of the smooth surface of the mantle (precentral, 

 Rolandic, intraparietal, parallel, olfactory, calloso-marginal), are very subject to modifi- 

 cation, as may partially be inferred from the detailed accounts which have already been 

 given. Although a considerable amount of attention has been paid by several observers 

 to these variations, and of late years especially by Pansch, Sernoff, Huschke. Riidinger, 

 Giacomini, Eberstaller, and Cunningham, it cannot be considered as proved that there is any 

 constant relationship between any of the variations which are found to occur, and either the 

 age, sex, occupation, or even the race of the individual. Various attempts have from time to 

 time been made to determine in particular a sexual distinction, but it has invariably appeared 

 that the inferences which had been drawn from an insufficient number of observations are not 

 borne out by a more extended series. It is more probable that certain racial differences may 

 ultimately be established when a sufficient number of brains belonging to individuals of 

 other than European races shall been carefully examined, but up to the present the materials 

 for such comparison have not been abundant enough. In brains of individuals belonging to 

 lower races which have been described (Bushmen, Fuegians, Lapps, and others), it has not 

 appeared that there is any distinct lack of complexity in the convolutions as compared with 

 ordinary European brains, but it is probable that if a large number were to be examined the 

 average complexity in such races would be below that of the average European brain. This 

 is in fact stated by Parker to be the case for the brain of the negro, but the number examined 

 were not sufficient to be considered conclusive. There is apparently, however, more distinct 

 evidence to show that complexity of convolution generally goes hand in hand with intellectual 

 development of the individual, for in many cases in which the brains of men of known 

 intellectual capacity have been examined, the complexity, due partly to the greater develop- 

 ment of secondary and tertiary sulci, partly tc the more curved course taken by the 

 principal sulci, has been decidedly, in some instances extraordinarily, marked. Indeed, 

 in some cases a relationship seems to have been apparent between a particular type 

 of mental development and a special part of the brain ; thus it was found that the brain 

 of the great French orator, Gambetta, showed an especial degree of complexity of the third 

 left frontal convolution. In skilled artisans it might be expected that the part of the brain 

 which is connected with the voluntary movements of the hands and fingers might be found 

 to be especially developed, and in one or two individual cases this has been noticed, but the 

 material for a general statement regarding such relationship is insufficient. Benedikt, from 

 the examination of the brains of a large number of individuals belonging to the criminal class, 

 was of opinion that there exists amongst these an undue tendency to the formation of four 

 antero-posterior convolutions in the frontal lobe, or in other words, an undue tendency to the 

 appearance of the paramesial and middle frontal sulci. Although apparently supported by a 

 few observations by other anatomists, this supposition has not borne the test of more extended 

 observation ; and, indeed, the so-called " criminal " type was actually less frequent in the 

 brains of convicts examined by Giacomini than in those of ordinary persons. 



