A few fissures and imperfectly developed convolutions were found upon the inferior sur face of the middle lobe, as well as upon the lateral and inferior surfaces of the anterior lobe.
The olfactory fissures were perfect but very small; the olfactory nerves appeared natural. The optic nerves were natural but small. The tuber cinereum was large and well developed.
The corpora mamillaria appeared to be fused together along the median line.
The pons Varolii very narrovv from before backwards ; the groove wilich passes along its middle was imperfect.
The corpus striatum was exceedingly small, and the groove between it and the optic thala mus was greatly increased in size. The t&nia semicircularis was large.
The convolution of the corpus callosum was very imperfectly developed. The hippocampus major was very small, and there could scarcely be said to be any trace of the hippocampus minor.
The fornix was well developed, as was also the corpus callosum. The longitudinal tracts on the surface of the corpus callosum were also well developed.
The pineal gland was large and situate very far forwards, corresponding very nearly to the middle of the optic thalamus. The quadri geminal tubercles seemed imperfectly deve loped, and the distinction between them was badly marked.
The optic tract was small, but natural in its 1 connections. The cerebellum was well deve loped : its laminw seemed natural. The lateral ventricles were large and rather dilated. The entire brain, after having lain in spirits for some days, weighed 1 lb. 41 oz. avoirdupois.
In some instances the hemispheres of the brain are fused together, there being little or no trace of a longitudinal fissure to separate them. This condition occurs generally in the Cyclopic monsters, or in monsters in which there is a total absence of the organs of vision. Where there is this singleness of brain there is also sometimes a fusion of the corpora striata and optic thalami of opposite sides together.
A total absence of all the transverse com missures of the brain constitutes, as Rokitansky observes, the opposite condition to that just detailed.
Idiotcy results from any change which im pairs to a material extent the structure of the hemispheres of the brain and of the fibres by which they are connected to each other, as well as to the other parts of the encephalon. All the' recorded instances of dissections of the brains of idiots shew that the evil consists in such an impairment of the hemispheres and their con voluted surface as must have materially pre vented their proper action. This may have begun in intra-uterine life or in infancy. The brain of infants at birth is far from being fully formed, and that part of it which is imperfectly developed is that upon which depends the mani festation of mental actions, namely, the hemi spheres of the brain and of the cerebellum ; the other parts, which are mostly concerned in phy sical nervous actions, are sufficiently perfect, being, however, generally small from the in fluence of the deficiency of the hemispheres.
Hypertrophy of the brain would occasion idiotcy, just as well as atrophy or imperfect developement of that organ (agenesie). Well marked cases of idiotcy resulting from the former cause are, however, as far as I know, yet wanting in medical records.
When there is a deficiency in any part of the cranial wall, a protrusion of a greater or less portion of the brain takes place—this consti tutes hernia cerebri or encephalocele. It is in point of size proportionate to the size of the opening in the cranium. The tumour is co vered externally. by the common integuments, and the displaced portion of the brain pushes before it the dura mater and the other mem branes of the brain.
The most frequent situation for hernia cerebri is in the occipital region of the head near the middle line, and next in point of frequency somewhere on the median line, where the bones of opposite sides remain for so long a time disunited : near the great fontanelle is a fre quent site of a protrusion ; sometimes it takes place on the side of the skull in the temporal region, or at the root of the nose. Such cases, however, are rare.