  In comparative and developmental neuroanatomy one encounters questions
regarding the deformation of neural tissue under stress. The motivation of this
note is an observation (Barbas {\it et al}) that at cortical folds or gyri, the
layers of neural tissue show relative thickening or thinning of upper or deep
layers. In general, the material properties of a slab of neural tissue are not
known, and even if known, would probably lead to a difficult problem in
elasticity theory. Here a simple argument is presented to show that bending an
elastic slab should produce a relative thickening of the layers on the inside
of the bend. The argument is based on the incompressibility of the material and
should therefore be fairly robust.
