Literary Notices. Ixxv 



Development of Associational Fibres of the Cortex.* 



It is a well-known fact that the medullated fibres connecting the va- 

 rious parts of the cerebrum do not all appear at the same time in the 

 course of embryonic development. Dr. Flechsig has one of his stu- 

 dents at work endeavoring to complete our knowledge of the exact 

 sequence. In a brief paper some of the results of this study as ap- 

 phed to the sensory connections are given. In the foetus at full term 

 the first associational bundles are developed in connection with those 

 portions of the occipital lobes which communicate with the fillet and 

 the ascending fibres from the pre-peduncle of the cerebellum. They 

 comprise short arcuate fibres which apparently never extend farther 

 cephalad than the central convolution and appear more distinctly in the 

 upper regions than in the lower. Examination of the brain of a child 

 of four weeks shows that there is a second cortical region aside from 

 the central convolution which is characterized by the early appearance 

 of well-developed associational systems. Its centre is in the region of 

 the lamina perforata anterior and the inner olfactory convolution. From 

 this point medullateded bundles go on the one hand to the thalamus 

 and basal striata [coronal fibres], and on the other hand to other grey 

 centres. 



Above all, numerous medullated tracts pass into the septum pellu- 

 cidum and the striae Lancisii which end in the small grey masses on the 

 dorsal surface of the callosum, and finally tracts to the uncinate gyrus. 

 The most strongly medullated bundle, however, hes within the gyrus 

 hippocampi passing caudad parallel to the surface from the cortex of 

 the gyrus uncinatus in the form of radial fibres into the cortex of the 

 gyrus hippocampi. Individual fibres may be followed up to the region 

 of the splenium, course under the ventricle outward and thus come 

 into the neighborhood of the rudimentary — poorly medullated — optic 

 radiation, with which they possibly penetrate the corpora quadrigamina. 

 This bundle is especially strong in that region of the gyrus hippocampi 

 which, on the basis of comparative anatomy, is regarded as the olfac- 

 tory centre, and there is in the whole brain no associational system 

 which can be even remotely compared with it for size. 



In view of the recent discovery that the olfactory cortex is phylo- 

 genetically so ancient, these facts acquire a special interest. The early 

 appearance of the striae Lancisii is especially suggestive after the dem- 



> Flechsig, P. Zur Entwickelungsgeschichte der Associationssysteme im 

 Menschlichen Gehirn. Berichte il. Verh. kl. Sack. Ges. d. Wiss. zu Leipzig. 

 Math.-Phys. Classe, 1894, 2. 



