MODEL OF MEDULLATED TRACTS IN BABY's BRAIN 127 



verse section the posterior limb corresponds to the lateral border 

 of the tail of the caudate nucleus, and the fibres first medullated 

 are projected straight to the cortex in a sagittal plane parallel 

 to the median sagittal plane and exactly midway between the 

 edge of the lateral ventricle and the surface of the island of Reil. 

 In the adult brain the plane of the primitive posterior limb of the 

 internal capsule can be demonstrated by making a sagittal section 

 along the lateral border of the caudate nucleus to the point where 

 it curves around into the roof of the lateral ventricle. In all of the 

 models there is a curious band labeled ''no. 37" on the cortical 

 radiation at the base of the central sulcus. This band shows 

 both in Barker's and in Flechsig's figures, quoted above, and in all 

 our series, thus it is probably a constant. I think that it is due 

 to the fact that the fibres curve lateralward just at the base of 

 the central sulcus, and from dissections of the fibres in the adult 

 brain I think that this bend in the fibres in due to antero-posterior 

 bundles of fibres near the median plane. With the exception of 

 this slight bend at the base of the central sulcus the primitive 

 posterior limb of the internal capsule consists of straight fibres, 

 I.e., those that take the shortest possible course. 



In the baby's brain, the lenticular radiation covers the entire 

 posterior limb (see fig. 4), while the thalamic radiation occupies 

 the middle third (see also fig. 4). In this particular specimen the 

 combined radiation extends only to the posterior central convo- 

 lution; in the series shown in Dr. Barker's figures, quoted above, 

 also from a new-born, the radiation reaches the anterior central 

 convolution as well, and this is true in brain figured by Flechsig^^ 

 from the a baby born one-half a month prematurely, and which 

 lived three weeks. I conclude, therefore, that the series from which 

 the model was made has a less extensive cortical radiation than 

 the usual brain at birth, and that, to represent the average, the 

 medullated bundle should be extended into the anterior central 

 convolution in the line 53 on fig. 4. From the series which we have, 

 I do not think that any of this radiation, even the part to the an- 

 terior central convolution, belongs to the pyramidal tract, the latter 



1^ Flechsig, Einige Bemerkungen ueber die Untersuchungsmethoden der Gross- 

 hirnrinde, insbesondere des Menschen. Arch. f. Anat. u. Phys., Anat. Abth., 

 1905. Taf. 16, fig. 8. 



