484 Dr Duckworth , Report on the brain of a 
(b) The corpus callosum has a genu and rostrum of similar 
form to those of the normal brain, except that the rostrum is 
rather thicker than usual. The abnormality of the corpus callosum 
consists in the extraordinary attenuation of the splenium and 
adjacent portion of the commissure (cf. Fig. 18). The gyrus of 
Retzius is therefore fully exposed, and the attenuation is doubtless 
due to the absence of interoccipital (visual), interparietal, and 
intertemporal fibres which should cross in this region. 
(c) The psalterium on the other hand is not reduced and 
the body of the fornix is rather thicker than usual : the corpora 
mammillaria seem to have been present, but the anterior pillars 
of the fornix have been destroyed in the process of injecting the 
brain. 
II. The uncus is normally developed. But the incisura 
temporalis is absent. The fimbria is normal and continuous as 
usual with the fornix. The fascia dentata is prominent and rises 
boldly to the surface behind the splenium to expand into the 
gyrus of Retzius (Balkenwindung). Thick striae of Lancisi are 
seen above the corpus callosum, and below the genu (anteriorly) 
fuse with part of the gyrus fornicatus to form a very definite gyrus 
subcallosus. 
III. Other gyri and sulci. The chief feature of interest is 
the remarkable sulcus splenialis 1 (Krueg) which, as in the lower 
Eutheria, forms a continuous furrow traceable from below the 
rostrum corporis callosi to a point just behind and rather below 
the splenium and gyrus of Retzius. Thence a short sulcus 
retrocalcarinus leads backwards to end apparent^ in the sulcus 
occipitalis inferior. But the true (and original) stem of the 
calcarine is rudimentary. In this respect the right hemisphere 
is absolutely different from the left. Two genual sulci are 
present and two or three smaller sulci indent the marginal gyrus. 
The left hemisphere (Plate XVII, Figs. IB, 2 B, 6, 7). 
The left is altogether larger than the right hemisphere, but is 
nevertheless much below the normal size. The anterior part of 
the temporal lobe is abnormal in respect of convolutions. 
The Sylvian fissure presents no anomalous features, save that 
the frontal and temporal opercula are not quite fully developed. 
(Some reserve must be made here since the brain was much 
damaged in this region during the process of injection.) The 
insula is thereby exposed in its posterior part, not anteriorly as 
in apes. 
Two orbital limbs, in addition to the anterior horizontal and 
ascending limbs can be seen. There is a sulcus subcentralis 
1 Intercalaris. 
