Turn up or cut off the rear end of one hemisphere so as to see clearly the optic tracts turning upwards towards the rear corner of the thalamus. The _corpora geniculata_ to which they also go, distinct in man, are less so in the sheep. The lower ones are visible between the optic-tract band and the 'testes,' however. * * * * * The brain's principal parts are thus passed in review. A longitudinal section of the whole organ through the median line will be found most instructive (Fig. 37). The student should also (on a _fresh_ brain, or one hardened in bichromate of potash or ammonia to save the contrast of color between white and gray matter) make transverse sections through the _nates_ and _crura_, and through the [Illustration: FIG. 37.--Median section of human brain below the hemispheres. _Th_, thalamus; _Cg_, corpora quadrigemina; _V^{III}_, third ventricle; _Com_, middle commissure; _F_, columns of fornix; _Inf_, infundibulum; _Op.n_, optic nerve; _Pit_, pituitary body; _Av_, arbor vitæ. (After Obersteiner). ] hemispheres just in front of the corpus albicans. The latter section shows on each side the _nucleus lenticularis_ of the corpus striatum, and also the _inner capsule_ (see Fig. 38, _Nl_, and _Ic_). [Illustration: FIG. 38.--Transverse section through right hemisphere (after Gegenbaur). _Cc_, corpus callosum; _Pf_, pillars of fornix; _Ic_, internal capsule; _V_, third ventricle; _Nl_, nucleus lenticularis. ] When all is said and done, the fact remains that, for the beginner, the understanding of the brain's structure is not an easy thing. It must be gone over and forgotten and learned again many times before it is definitively assimilated by the mind. But patience and repetition, here as elsewhere, will bear their perfect fruit. CHAPTER VIII. THE FUNCTIONS OF THE BRAIN.