84 The Development of the Sensory Tracts [CHAP. 



lateralis of the thalamus and from Flechsig's cup-shaped body (schalenfbrmiger Korper), 

 and to terminate exclusively in the two central gyri (vide infra). This set is recognisable 

 immediately behind the place to be filled later by the fibres of the pyramidal tract, and some 

 offshoots course in the external capsule and lamina medullaris externa of the lenticular nucleus. 

 The second set becomes medullated a month later and its fibres, derived from both the nucleus 

 lateralis of the thalamus and the "centre median" of Luys, chiefiy proceed to the central gyri, 

 the paracentral lobule and the base of the superior frontal convolution, while some bend 

 round into the gyrus fornicatus and cornu ammonis. The third set runs in the middle of 

 the internal capsule and is destined for the inferior frontal convolution, the gyrus fornicatus, 

 the anterior half of the upper frontal and the base of the middle frontal gyri. 



Of these sets of fibres, the first is the only one which need concern us here, because 

 although Flechsig is evidently unable to describe its origin definitely and apart from other sets 

 of fibres arising from the red nucleus and from other structures in this situation, and can only 

 give us a diagrammatic representation of its course, there seems no doubt that he regards it 

 as the main continuation of the lemniscus proper, and that it is to these fibres he refers 

 when he says that "the lemniscus (Hauptschleife) terminates in the central convolutions and 

 exceptionally in the anterior portion of the superior parietal gyrus"; and, further, "that, in 

 man, many more sensory fibres proceed to the ascending parietal than to the ascending frontal 



In spite of his pointed remark to the effect that the postcentral gyrus is the receiver 

 of more sensory fibres than the precentral, Flechsig has firmly advanced his histological results 

 in support of the hypothesis of the functional unity of the two central convolutions, but it 

 will be interesting to hear whether, in face of Professors Sherrington and Griinbaum's 

 findings, further observations or a re-examination of his specimens will cause him to modify 

 his statements. 



Another worker whose developmental studies have received attention is Dollken, but he 

 has only made use of the brains of the dog and cat, and his observations, although interesting 

 from the phylogenetic standpoint, do not assist us in solving the question at issue. Similarly, 

 as I mentioned in my last chapter, the more recent work of Hosel has not enlightened us. 



Professor and Madame Vogt also are including in their programme a research on the 

 medullated nerve fibres in the developing brain of the human being as well as other animals, 

 and recently have published an atlas giving faithful reproductions of many of their specimens. 

 Unfortunately the letterpress of this work, or rather that pertaining to the sections of the 

 human foetal brain, is not yet completed, and consecjuently I am unable to refer in detail to 

 a special band of fibres figured in their drawings and evidently standing in close relation with 

 the postcentral gyrus. But this band of fibres is of special interest to me, because it looks 

 as if it might possibly give us a clue to the true distribution of the " cortical lemniscus." In 

 sagittal sections of the foetal brain of a suitable age the fibres to which I refer appear as a 

 rather thin but compact dense band, springing from the centrum ovale and climbing up the 

 Rolandic side of the medullary projection of the postcentral gyrus; and in a conversation which 

 I had recently with Professor and Madame Vogt, I was led to understand that this strange 

 band becomes medullated at a relatively early period, and on that account can be distinguished 

 from the mass of fibres pertaining to the precentral gyrus, with which it runs parallel and 

 in close connection ; furthermore, the individual fibres of this tract are of large calibre, and 

 there seems no doubt that their presence explains the large fibres which I have described as 



