vi Proceedings. \^Odober iStli, igio. 



around each of these primary sensory territories to elaborate, as it 

 were, the raw material received by the latter, and also to blend the 

 various impressions, visual, auditory, tactile, olfactory, et cetera, of 

 one object into a consciousness of all its properties, and to test 

 and appraise their significance in the light of previous stimula- 

 tions, the effects of which have been stored up in the various 

 cortical areas. 



Thus it comes to pass that the cortex is mapped out into a 

 great number of territories, differing in structure and function, 

 and varying in size in ditTerent mammals, not only because the 

 sense-organs themselves vary in size and acuteness in different 

 creatures, but also because in different orders and families a 

 sense organ of a given size will have a varying cortical representa- 

 tion. Thus, if one were to take a dog and a baboon with eyes 

 of the same size, the monkey will be found to possess a much 

 larger cortical visual area than the dog. 



It is these differences which determine the varied plans ol 

 cortical folding and the resulting varieties in the patterns of the 

 convolutions in different mammals. 



Folding occurs most often along the boundary line between 

 two areas of different structure and function. The difference in 

 the rate of expansion of two such areas is no doubt the reason 

 for this type of fissure formation- — limiting sulci. 



In the second place a rapidly growing cortical territory, 

 meeting with obstruction to its expansion on all sides, may 

 become buckled in, and so a furrow develops along its axis 

 {i.e., within its area), instead of at its edges. This second class 

 of furrow is much less frequent than the first class, and may be 

 distinguished as the group of axial sulci. 



There is a third variety, which may be called the operculated 

 sulcus, in which one lip projects over a submerged area. Sulci 

 of this type are produced by the submerging of a specialised 

 fringing territory surrounding a main sensory area. 



In the fourth place various mechanical factors come into 

 operation to modify the form of furrows formed in one of these 

 three ways, or even to produce new sulci. 



