i8o THOMPSON YATES LABORATORIES REPORT 
3. Posterior commissure and lamina commissuralis mesencephali. 
4. Transverse fibres of the optic vesicle. 
5. Mesencephalic system of fibres. 
6. Tracts of the spinal cord. 
I. The Tracts in Connection with the Great Cell Mass of the 
Hemisphere include : — • 
[a) Tractus septo-mesencephalicus or pallial system. 
[If) The striate tracts (tr. strio-mesencephalicus and tr. strio-thalamicus). 
(c) Tractus occipito mesencephalicus. 
{d) Tractus occipito frontalis, 
{e) Commissura anterior. 
(a) Tractus Septo-mesencephalicus or PalUal System * 
The great mass of the cerebral hemisphere is formed by the corpus striatum, a ganglionic 
mass of densely-packed cells of ovoid shape. The cells are grouped in clusters, and, as shown by 
the Nissl method, each cell contains a very large nucleus (fig. 54, Plate X). 
The pallium which lies over the corpus striatum consists of a thin plate of nervous matter 
forming the mesial and dorsal wall of the ventricle ; laterally it gradually loses itself in the 
substance of the corpus striatum. It contains the fibres of an important tract described by Bumm 
under the name of ' Markbiindel der strahligen Scheidewand ' or ' Tractus Septo-mesencephalicus ' 
(Edinger). This fan-shaped tract is superficial, and covers a large part of the posterior and 
mesial aspect of the surface of the brain (Plate IV, figs, i, 2, 3, &c.). 
The main mass of the tract converges in front of the anterior commissure (fig. 15, Plate 
VI), then turns sharply outwards to become superficial, and bends round the tractus striothalamicus 
(figs. 9, 10, II, Plate V). It remains superficially situated in the dorsal and lateral aspect of the 
thalamencephalon. Transverse sections show that it can be traced down as far as the junction of 
the thalamus with the optic lobes (fig. 27, Plate VII ; figs. 35-37, Plate VIII). BuMM,t in his 
original description, states that the tract ends in the region between the lateral part of the cortext 
of the corpus-bigeminum and the corpus-opticum. EdingerJ states that it disappears in the most 
frontal section of the roof of the middle brain. We have not succeeded in tracing the tract quite 
so far as these authors, and incline more to the view of Munzer and Wiener, who were unable 
to follow it further than the epithalamic region. Horizontal sections show that, although the 
great mass of fibres composing the tract are contained in the pallium, there is a special group 
which is in connection with the anterior part of the cell mass of the hemisphere (figs. 3 and 4, 
Plate IV). 
Whilst the major part of the tract converges to pass in front of the anterior commissure, a 
definite and smaller portion passes posteriorly to this commissure (figs. 13 and 16), and enters the 
thalamic region. 
* This tract is lettered A in the figures, and appears in a very large number of the sections, 
t Loc, cit. J Loc, cit. 
