220 On .some Association Truetx of Fibres [CHAP. 



and occupy the frontal division of the internal capsule near the genu; and then, having passed through 

 the crus cerebri, internal to the main motor tract, they terminate in the pons. As to the impulses conveyed 

 by the tract, Flechsig is of opinion that it is concerned with the movements of bilaterally innervated 

 muscles, and that it includes motor speech fibres 1 . 



To me the feature of greatest interest concerning this tract, as described by Flechsig, is the assigned 

 field of origin, the hinder portion of the three frontal gyri and perhaps the middle of the gyrus fornicatus, 

 for one is immediately struck with the point that, leaving out the gyrus fornicatus, it virtually coincides 

 with the extent of the " intermediate precentral " field of cortex. Bearing in mind the histological .structure 

 of this part with its large pyramidal cells and large nerve fibres, one cannot fail to appreciate the force 

 of Flechsig's statement that the tract originates from the large cells here situated and is composed of their 

 axous; and von Monakow's well-known example of degeneration of the tract secondary to a lesion of the 

 hinder part of the middle and lower frontal gyri must be acknowledged in favour of this assumption. Never- 

 theless it has to be mentioned that this origin is not generally accepted, for Dejeriue excludes the upper part 

 and confines the source to the Rolandic and adjacent frontal operculum, while Zacher attaches importance 

 to the cortex of the insula; their respective grounds for doing so, however, need not be detailed. 



Looking upon tha above-described fasciculus as a projection tract, I have now to mention some bands 

 of an associating nature. 



The Tapetum. 



The best account of the connections of the tapetum is that given by Dejerine ; by this observer it is 

 called the fasciculus occipito-frontalis, the whole cortex of the frontal lobe is said to give origin to it and 

 passing backwards in a position mesial to the corona radiata it is said to be distributed to the cortex 

 covering the lateral surface and inferior border of the occipital lobe, a field corresponding, by the way, 

 with that which I have called "visile-psychic." But although Muratow has seen degeneration in the tapetum 

 after lesions of the frontal lobe, and although the whole of the frontal lobe is given as its source, I do 

 not know of any evidence, one way or the other, to show that it has special connections with the area 

 in which we are at present interested ; still we are compelled to take notice of it because it is such a 

 well-known tract. The controversial question of the relation of the tapetum to the corpus callosum does not 

 concern us. 



The Fasciculus Longitudinal is Superior. 



Like the tapetum, the fasciculus longitudinalis superior is supposed to couple the frontal ami occipital 

 lobes, but it lies lateral instead of medial to the corona radiata. Its fibres are said to vary in length 

 and to be for the most part short. A portion of the tract is figured as following an arciform pathway, 

 placed above the level of the insula, by which the lower frontal cortex becomes connected with the upper 

 temporal ; and in the left hemisphere, in connection with the function of speech, much importance is attached 

 to this association. 



Fasciculus Uncinatus. 



The exact origin and destination and likewise the functions of the fasciculus so named are obscure ; 

 curving beneath the limen insulae, by some it is said to pertain to the rhinencephalon, while others assert 

 that it associates the tip of the temporal with the base of the frontal lobe. 



Xhort Association Tracts. 



In addition to these long association tracts possibly having connections with the "intermediate precentral" 

 area, short bands, the fibrae propriae, are to be reckoned with as connecting adjacent convolutions and parts ; 

 thus by means of commissural horizontal fibres corresponding levels of the "intermediate" and "precentral" 

 areas are brought into association, and in the same way the " intermediate" cortex is connected with more 

 anterior parts. Similarly, vertically-placed fibres couple different levels. 



1 A further supposition is that, by means of an extension of neurones from the poutine nuclei to the cerebellum, 

 it serves to throw the latter under the influence of the opposite cerebral hemisphere. 



