1904.] On the Localisation of Cerebral Function. 391 



motor area on the parietal side. In man and the man-like ape, an 

 unnamed but constant fissuret, situated on the paracentral lobule, 

 immediately below and in front of the upper extremity of the fissure 

 of Eolando, is looked upon as the homologue of the sulcus cruciatus. 



Visual Area. Showing how greatly the lower mammal relies on 

 sight in the contest for survival, quite one-sixth of the brain surface 

 is allotted to visual cortex. Architecturally it is astonishing how 

 closely the human plan is followed. The lessons in homology learned 

 are, that the " true calcarine " fissure (Elliot Smith's nomenclature) of 

 lower mammals is the antecedent of the anterior calcarine fissure or 

 " stem " of Homo, that the intercalary sulcus does not develop into 

 the calloso-marginal of man, but undergoes retrograde changes, that 

 the ' posterior calcarine fissure may continue as such, and that the 

 suprasplenial sulcus of Canis and Felis (the so-called " lateral " sulcus 

 of Sus) is the derivative of the human fissura extrema of Seitz (the 

 Simian " sulcus intrastriatus lateralis "). The research throws no- 

 light on the problem of the " Affenspalte." 



Postcrudal oi' Sensory Area. The postcrucial or sensory field forms, 

 a morphological buffer to the crucial or motor, and is maintained to be 

 the homologue and analogue of the postcentral area in primates. 



Lobus Pyriformis and Hippocampal Region. The variations in distribu- 

 tion of the different types of cortex found hereabouts are contrasted in 

 the microsmatic and macrosmatic brain. 



Limbic Area. It is found that types of cortex akin to those 

 recognised in man are repeated in the lower mammal. The genual 

 fissure is taken as the homologue of the calloso-marginal. 



Parietal Area. Histology suggests that this field is the forerunner 

 of the parietal area in Homo, and that its cortex is older, in the sense 

 of phylogeny, than frontal cortex. Support is given to the assumption 

 that the lateral sulcus, as seen in most mammals, is the antecedent of 

 the intraparietal sulcus of primates. In Sus, the so-called "supra- 

 sylvian " sulcus is really the lateral, the true suprasylvian sulcus being 

 both placed at a lower level and rudimentary. 



Ectosylvian Region. Out of the ectosylvian region of lower mammals* 

 is developed the sylvian region, including the insula, and much of 

 the temporal lobe of primates. A small field investing the so-called 

 fissure of Sylvius of lower mammals appears to be the analogue of the 

 " audito-sensory " area of man and the homologue of the transverse 

 temporal gyri. From this as a basis important deductions can be drawn. 



Frontal Lobe. The types of cortex which characterise the frontal 

 lobe in man are not represented in lower mammals. 



Some General Conclusions. The stability of the architectural plan of 

 any given field of cortex is directly related to the phylogenetic age 

 of that cortex and to the importance, as a means to survival, of the 

 function it subserves. 



VOL. LXXIV. 2 G 



