MODEL OF MEDULLATED TRACTS IN BABY's BRAIN 133 



lateral nucleus (fig. 3). The dorso-lateral nucleus is entirely 

 non-medullated at birth. 



The pulvinar (no. 51), as has just been said, is the projecting 

 caudal part of the dorso-lateral mass. Its caudal boundary is the 

 posterior commissure (no. 40, fig. l);ventrally it is readily marked 

 off from the center median of Lays (fig. 3) and laterally it extends 

 to the taenia semicircularis (fig. 1), but it has no cerebral border, 

 since it is continuous with the dorso-lateral nucleus (figs. 3 and 5). 



On the lateral surface of the thalamus are the two geniculate 

 bodies, the medial and lateral. They are both oval masses of cells 

 whose form is well seen from the surface (nos. 49 and 50, fig. 9). 

 The medial geniculate body has no medullated fibres in this series 

 but the lateral geniculate body has a band from the optic nerve 

 which in part spreads on to the surface, but which for the most 

 part curves around the inner border, just caudal to the medullated 

 thalamo-cortical bundle. This shows in the figure quoted above 

 from Barker. A part of these fibres seem to enter the geniculate 

 body, a part the pulvinar. 



The center median of Luys is well shown in figs. 1, 3, 4. It 

 is an oval mass of cells which lies in caudal part of the thalamus 

 near the median line. It is just dorsal in position to the red nucleus, 

 lateral to the fasciculus retroflexus of Meynert and lies between 

 the medial nucleus, the ventro-lateral nucleus and the pulvinar. 

 It fits into the cup-shaped nucleus as can be best seen in fig. 11, 

 and in common with it receives a mass of medullated fibres con- 

 sisting of a part of the medial lemniscus, possibly of fibres from 

 the red nucleus, and of a small tract from the nucleus of the in- 

 ferior colliculus. It has no other medullated tracts at birth. 



This corpus striatum is of course made of the well known parts, 

 the caudate and the lenticular nucleus. The form of the caudate, 

 with its swollen head and its curved tail is well known and can 

 be readily seen in the models. The best way to obtain an idea 

 of the caudate nucleus is to take an adult brain well hardened in 

 formalin and shell the nucleus out from the bed of fibres, the 

 internal capsule, on which it rests. The form, and the rela- 

 tions of the lenticular nucleus are much harder to make out. 

 Starting from the lateral view of the baby's brain (fig. 10), the 



