188 Cortical Structure of the Gyrus Fornicatus [CHAP. 



and ray chief reason for this assumption is that cells of a similar description are to be 

 found, as I have already mentioned, in the lobus pyriformis. 



Other Boundaries of the Common Limbic Area. 



Above the corpus callosum the mid-limbic division of the calloso-marginal sulcus may 

 be regarded as a boundary, although an inconstant one, for the limbic characters may fall 

 short of or transgress this sulcus. 



Along this stretch the field is in contact in turn with the frontal, intermediate precentral 

 and post-central areas and the structural differentiation presents no difficulty. Further back 

 the post-limbic sulcus serves as a rough line of separation from the parietal cortex, and 

 in the neighbourhood of the splenium the visuo-psychic, hippocampal, and fornicate types 

 of arrangement find a meeting-point. 



Some Associations of the Various Areas described. 



It may help to complete this histological account if I make brief allusion to the 

 connections which these parts have with other parts of the brain. The determination of 

 these connections has of course not come within my field of study, and the following remarks 

 are derived from the researches of those who mainly in the case of the lower animals 

 have given time to this subject. These investigations show that the associations formed 

 by these fields are of an extremely intricate and complex character, so intricate that I must 

 content myself with merely naming them, and for details refer the reader to the works 

 of S. Ram<5n y Cajal, Barker, Zuckerkandl, etc. 



To begin with, there are close associations between the cell-elements of the cortex of 

 the lobus pyriformis and those of the subiculum and cornu ammonis, and possibly also of 

 the nucleus amygdalae. 



In the posterior direction the cornu ammonis receives or gives off fibres which find 

 a pathway, first, in the occipital end of the striae supracallosae (Ramdh y Cajal), and 

 secondly, in the posterior prolongation of the cingulum (the band of fibres which, underlying 

 the gyrus fornicatus, appears to unite cells in that gyrus with those of the cornu ammonis). 

 Further, the cornua ammonis of the two hemispheres seem to be united by means of the 

 psalterium. Then by way of the fornix the cornu ammonis, and indirectly the lobus 

 pyriformis, establishes connections with the corpora mammillaria, the nucleus habenulae, the 

 optic thalami, and septum pellucidum. I have already mentioned that through the anterior 

 commissure primary olfactory neurones gain associations with the structures of the opposite 

 hemisphere, and there are many further complicated connections which it would be purposeless 

 to mention here. 



EXAMINATION OF THE LIMBIC CORTEX IN THE ANTHROPOID BRAIN. (Plate II.) 



Before proceeding to a discussion of the functions of the various areas dealt with in 

 the foregoing pages I shall here intercalate a brief reference to the structure of the same 

 parts in the anthropoid brain, viz., that of the chimpanzee and orang. 



As the anthropoidae resemble man in possessing an olfactory apparatus which has 

 dwindled down to a mere fraction of what exists in lower mammals, it is not surprising 



