1888.] Dr A. Bruce on Absence of Corpus Callosum. 339 
fig. 30, drawn from the brain sent me by Dr Buxton, pathologist of 
Wadsley Asylum, in which the anterior two-thirds of the corpus 
callosum had completely atrophied in consequence of a lesion affect- 
ing the centrum of ovale of the frontal and part of the parietal 
lobes). Had this fronto-occipital association system been merely con- 
cealed by the corpus callosum, it should now be as prominent as in 
the cases of congenital callosal defect. It need not, I think, surprise 
us that this structure does not contain grey matter. We find what 
is undoubtedly septum lucidum contains only white longitudinal 
fibres, and in the fornix and nervus Lancisii we see the tendency 
to the formation of the marginal arch into longitudinal fibres. The 
causes of the arrested growth are very various, and must act at 
different stages of development. The principal factors concerned 
are the primitive falx and the septa lucida. Unfortunately, few of 
the records permit of our determining the cause in any given case, 
so that the hypotheses stated below are intended principally to aid 
future investigators. The causes may depend on^ — 
1. The primitive falx cerebri — (a) its non-development during 
the first three weeks of life ; (h) after its formation its excessive 
resistance to atrophy, such as might result from intra-uterine lepto- 
meningitis ; (c) a permanently too deep position of the falx, such as 
might result from cranial deformity (Richter, Virchow's Aixhiv, 
106). Richter considers that premature ossification of the basis 
cranii increases the angle between the two petrous temporal bones, 
and by thus stretching the tentorium cerebelli so depresses the free 
border of the falx that it divides the corpus callosum as it grows 
up against it. 
2. Irregular distribution of the anterior cerebral arteries (Sander) 
passing between the septa lucida, and preventing their union. 
3. Asymmetry of the hemispheres (resulting from asymmetry of 
cranium), so that the two septa lucida are not opposite each other. 
4. Abnormal growths in the falx. 
5. Nutritional disturbance in septa lucida, such as early hydro- 
cephalus. 
As causes of secondary defect are dropsy of the fifth ventricle 
(Mitchell Henry), hydatids, lesions in callosal arteries (Kaufmann 
and Eichler), in vessels of centum ovale. 
Several authors imagine that the area rh represents the stump of 
