860 MR HAROLD AXEL HAIG ON THE 
the grey matter surrounding the aqueduct shows mesioventrally the nuclei of the 3rd 
nerve, and ventral to the latter the posterior longitudinal bundles are fairly obvious. 
The crustze are of less extent than those of the former section. 
The posterior commissure of the brain shows dorsal to the aqueduct of Sylvius, and 
is of moderate antero-posterior dimensions. 
Points of comparative value in connection with the medulla, pons, and mid-brain 
are as follows :— 
(a) The disproportion between the transverse and antero-posterior diameters of the 
medulla, the former being about twice or two and a-half times the length of 
the latter. 
(b) The relatively large proportion of grey matter in all these regions, much of it, 
however, being composed of purely neuroglial tissue. 
(c) The aberrant shape of the olivary nucleus and the outward displacement of the 
whole olive. 
(d) The marked development of the restiform body and its early distinction in a 
comparatively low region. 
(e) The late formation of the crustze, the mid-brain being reached before these are 
well defined. Other minor points will be made out by reference to Plate L., 
and comparison of the figures with sections of normal human material. 
V. Tue Hisrovocy or THE Opric THatamus. (Text-fig. 4.) 
The main features to be made out from a vertical (sagittal) section of the optic 
thalamus consist mainly in the relative distribution of grey and white matter; the 
white matter occurs in two main masses—an external, thick superiorly and thinning off 
towards the anterior aspect, and an internal oblique mass which divides the internal 
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Fic. 4.—A mesial sagittal section of the optic thalamus (semidiagrammatic). x 4 times. 
w.f. Superficial layer of white fibres into which septa of neuroglia pass from the deeper grey matter. 
n.n.n. Groups of large nerve-cells in the grey matter. 
g.m. Central grey matter. The internal mass is not sharply differentiated into grey and white 
matter; small nerve-cells appear scattered throughout the former. 
