CHAP, ii.] THE BRAIN. 981 



important portion called the pulvinar y into which the hind part of 

 the median nucleus merges ; this is partly imbedded in the crus 

 ventrally and in the hemisphere laterally, and is partly free, 

 coming to the surface beneath the hind end of the corpus callosum. 

 In a median longitudinal section of the brain (Fig. 120), it is the 

 pulvinar which forms the cushion-like (hence the name) end of the 

 thalamus beneath the overhanging splenium of the corpus cal- 

 losum, by the side of the pineal gland ; and in the horizontal view 

 (Fig. 115, Pvr), in which the hemispheres are supposed to have 

 been removed, the same pulvinar is seen projecting over the crus 

 by the side of the anterior corpus quadrigeminum. The buried 

 portion of the pulvinar is exposed in a transverse section taken 

 through the anterior corpus quadrigeminum, Fig. 114; the extreme 

 end of this part of the pulvinar (Pvr) is here seen lying dorsal and 

 lateral to the pes of the crus, immediately above two masses of 

 grey matter, the corpora geniculata (Ggl. Ggm.), of which we shall 

 speak later on. One of these, the lateral corpus geniculatum 

 (C.g.l.), is especially connected with ;bhe optic tract (op), and, as 

 we shall see hereafter, the pulvinar itself is also connected with 

 the optic tract and is an important part of the central apparatus 

 of vision. 



629. The substantia nigra, the red nucleus and other grey 

 matter of the tegmentum. Nerve-cells and groups of nerve-cells, 

 or areas of grey matter, too small to deserve special names, 

 are scattered throughout the tegmentum along its course. But, 

 besides these and the nuclei of the third and fourth cranial nerves, 

 of which we have already spoken, certain larger collections of grey 

 matter deserve attention. A conspicuous mass of grey matter, 

 circular in transverse section, placed in the midst of the tegmentum 

 on each side but somewhat near the middle line, and stretching 

 from the hinder margin of the third ventricle beneath the anterior 

 corpus quadrigeminum (Figs. 114, 115), is, from the red tint it 

 possesses, called the red nucleus, nucleus or locus ruber. It is 

 traversed by fibres of the third nerve as these make their way 

 ventrally from the nucleus to the surface. 



We must consider also as belonging to the tegmentum a 

 large area of grey matter, somewhat lens-shaped in section (Fig. 

 114, Sn) which lies between the pes and tegmentum, sharply 

 marking off the one from the other. From its dark appearance 

 due to the abundance of black pigment it is called the substantia 

 nigra or locus niger. It acquires its largest dimensions at about 

 the middle of the length of the crus, coming to an end in front 

 (Fig. 116, Sri) and fading away behind (Fig. 113) as the crus 

 passes beneath the posterior corpora quadrigemina. These two, 

 the red nucleus and the substantia nigra, are perhaps the most 

 important collections of grey matter in the tegmentum, but we 

 may add that at the front of the crus as the substantia nigra 

 comes to an end there is seen in a somewhat similar position 



