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1888 .] Dr A. Bruce on Absentee of Gor'pus Callosum. 
The corpus callosum was entirely absent. The septum lucidum 
and fornix were apparently absent ; but, placed more laterally than 
these structures, and overhung by the grey matter of the cortex, 
a triangular area of white matter (which has the size represented 
in the drawing — spt. fig. 2) lay between the anterior commissure 
below, the free edge of the grey matter (of the gyrus fornicatus ?) 
in front and above, and the tela choroidea (not shown) and optic 
thalamus behind and below. This area has several shallow longi- 
tudinal grooves. Its lower rounded margin is formed by a structure 
which is undoubtedly the fornix (ascending limb). This triangular 
area is almost certainly the septum lucidum (see below). 
Transverse vertical sections of left hemisphere (fig. 3) made 
immediately anterior to the triangular area of white matter {spt. 
fig. 2), and through the anterior cornu of the lateral ventricle. 
c.n, caudate nucleus j l.n, lenticular nucleus ; i.c, internal capsule 
{of quite normal size and appearance ) ; c.r, fibres of corona radiata 
curving from internal capsule upwards and mostly inwards, towards 
grey matter of convolutions, almost no fibres traceable into the dark 
area spt ; spt, a dark area of fibres having mostly antero-posterior 
direction regarded as a forward continuation of fibres of spt. (fig. 2), 
and as belonging to septum lucidum ; l.v, anterior cornu of lateral 
ventricle \ f between l.v and spt, white fibres running upwards and 
outwards, and then entering tract spt., and possibly belonging to 
fornix system (a similar strand seen in brain of kangaroo — Beevor) ; 
e.c, external capsule ; cl, claustrum ; f.s, fissure of Sylvius. 
Fig. 4. Transverse section at level of anterior commissure, a.c, 
anterior commissure (of normal size) ; /, fornix ascending limb 
(relation to spt. should be noted); spt, an area of white fibres — 
mostly having a longitudinal direction — a few strands crossing it 
transversely, cannot (microscopically) be traced further than a dense 
network at its outer edge ; c.s, a shallow fissure between spt. and 
gyrus fornicatus {g.f), regarded as representing the callosal sulcus; 
i.c, internal capsule — careful examination shows to be quite normal 
size; c.r, coronal radiata — passing upwards and inwards. Many 
fibres traced into {g.f.) gyms fornicatus. A few seemed to enter 
the network outside area spt. 
Fig. 5. Transverse section, made at posterior limit of the tri- 
angular area spt. (fig. 2), and about the middle of optic thalmus ; 
