MODEL OF MEDULLATED TRACTS IN BABY's BRAIN 131 



better in these sections than in those of the other model where it 

 was incomplete. The sagittal sections show its length, that it 

 is a thin mass curved to fit into the hollow formed by the crus, 

 and that it extends to the nucleus hypothalamicus of Luys which 

 is a small lens-shaped body lying between the zona inserta and 

 the internal capsule. The cerebral surface of the substantia 

 nigra is curved, indented as it were by the hypothalamic nucleus 

 of Luys. Along the lateral border of the substantia nigra is a 

 tiny medullated bundle, shown only in fig. 9, which appears to 

 connect the substantia nigra with Luys' body. 



The nuclei of the thalamus that can be modeled out, are es- 

 sentially those described by Burdach^^ and more recently by Sachs, 

 and Roussy.^^ In fig. 1, are seen especially the anterior and medial 

 nuclei. Neither of them show any medullated fibres whatever. 

 The medial nucleus (no. 55), covers the floor of the third ventricle; 

 it can not be separated from the pulvinar, nor in sagittal sections 

 at birth is it possible to separate it from the dorso-lateral nucleus 

 along the dorsal border of the thalamus, as is plain in fig. 1. 

 In the sections (figs. 5 and 7), it will be noted that there is a pale 

 band, which represents non-medullated fibres extending forward 

 from the center median of Luys to the anterior nucleus (56) of 

 the thalamus and separating the ventro-lateral nucleus from 

 the dorso-lateral nucleus. In the zone of the median nucleus 

 this non-medullated band entirely disappears. The thickness 

 of the medial nucleus from the middle line toward the side, is 

 only a very small proportion of the width of the thalamus, as 

 can readily be seen in fig. 1, since the caudal part of the nucleus 

 has been cut away to expose the center median of Luys and the 

 ventro-lateral nucleus. In the zone just cerebralward to the 

 center median of Luj^s, the medial nucleus is thicker than it is 

 along the ventral border in fig. 1, and hence it is seen in sagittal 

 sections at the level of Dejerine's fig. 269, vol. 1. 



The ventro-lateral nucleus of the thalamus is the largest mass 

 of cells. It is shown best in fig. 3, from which the medial nucleus 



" Burdach, Bau und Leben des Gehirus. Leipzig. 1822. Dykschen Buchhand- 

 lung. B(l. 2. 

 1' (Roussy, La Couche Optique, Paris. G. Steinbeil, Edituer, 1907. 



