CHAPTER VII. 



LIMBIC LOBE. 



CONSTRUING the word limbic in the wide sense given it by Broca, I shall now describe 

 the cortical structure of the various subdivisions which comparative anatomy and other studies 

 have suggested as constituents of Broca's " grande lobe limbique." In this conception of the 

 lobe the following parts arc embraced, the olfactory lobe, the whole gyrus hippocampi (including 

 the dentate gyrus, uncus, and pyriform lobe), the entire gyrus f'ornicatus, and other subsidiary 

 structures which will be referred to in the course of our description. 



Chiefly from studies in comparative anatomy the conclusion has been arrived at that 

 certain portions of the limbic lobe govern the olfactory sense : it has also been assumed, on less 

 secure grounds, that other portions preside over the sense of taste, but whether the whole 

 limbic lobe subserves these functions, and exactly how the functions are distributed, are still 

 unknown. However, as we possess more knowledge regarding olfactory than gustatory localisa- 

 tion, I shall open my remarks with an account of the cortex which in all probability governs 

 the former sense. 



It is not my intention to deal with the structure of the olfactory bulb and peduncle, 

 as this is a part of the olfactory apparatus which has received thorough attention at the 

 hands of many other observers, but it will be useful for future guidance to give a brief 

 outline of the apparent destination of the various sets of fibres arising from cells in the 

 olfactory bulb and proceeding in the olfactory peduncle towards the brain. The distribution 

 of these fibres has been studied chiefly in lower animals, but we have no reason for believing 

 that the arrangement is not homologous in man, and the fibres may be described as issuing 

 in three sets. 



(1) One fasciculus passes deeply beneath the mesial root to gain the anterior commissure 

 and proceed to the opposite hemisphere. 



(2) Another set enters the mesial root and soon sinking into the cortex splits up to 

 gain the following parts, (a) the grey substance of the trigonum olfactorium (Calleja) (a part 

 rudimentary in man but well-developed in many other mammalia and known as the tubercuhim 

 olfactorium or tubercle of the olfactory tract), (It) the gyrus subcallosus and anterior or pre- 

 genual part of the gyrus f'ornicatus, (c) the area parolfactoria of Broca, and (d) the septum 

 pellucidum. 



(3) The third set passes along the lateral root and sinks into the anterior end of the 

 lobulus pyrit'ormis (Ramon y Cajal) to form connections with cells to be described hereafter. 

 According to Flechsig these fibres end in the superficial large cells here situated, but according 



