The selective vulnerability of the cornu ammonis of the human brain in various pathologic conditions, such as epilepsy, dementia paralytica, circulatory disturbances and carbon monoxide poisoning, has been attributed by Spielmeyer and others1 to peculiarities in the local blood supply.2 These investigators brought forward various explanations to show in what way the vascularization of the region is the decisive factor in this vulnerability.
The vascularization of the cornu ammonis is poor (Spielmeyer and Uchimura3). Its margin of safety is, therefore, smaller than that of other parts of the brain. Thus, in a case of circulatory insufficiency the nerve cells are inadequately supplied and disintegrate before the cells in other parts of the brain, where the capillary bed is richer, begin to suffer.
The cornu ammonis, particularly the most vulnerable area known as Sommer's sector, is said to be supplied by a blood vessel (Uchimura4), or rather by