The acephalic state is very frequent. It is always associated with complete or nearly com plete absence of the cranial bones, and frequently more or less of those of the spine. In some the trunk and extremities are perfect, but in very many there are deficiencies to a greater or less degree in the formation of these parts.
In anencephalia there is a defective state of encephalon, but not an absence of it ; and it seems highly probable that this condition is due, not so much to an original arrest of deve lopement as to the occurrence of an hydroce phalic state at an early period of intra-uterine hfe, the accumulated fluid breaking down the newly formed nervous matter, which wants the support of the cranial bones.
The extremest degree of this defect is when a large portion of the cranial bones is wanting, and also when there is a large fissure in the spine. In other cases the spinal fissure does not exist. 'The cranium is largely open on its posterior and superior aspect, the head thrown back, the neck very short and thick, the eye balls very large and prominent, and the mouth partially open, giving to the features a very hideous expression.
The hollow of the base of the cranium is, in these cases, filled up by a red, soft, highly vas cular substance, continuous with the pia mater of the spinal cord. This, in general, appears to be nothing more than the cranial pia mater, which has collapsed into this state by the de struetion of the nervous matter, and in which sometimes small masses of nervous matter may be discovered here and there. It is covered by a smooth membrane, which inay be an imper fect arachuoid. In some instances, however, the tumour is of considerable size, more volu minous, according to Geoffroy St. Hilaire, than even the normal brain. It is disposed in lobes, which resemble somewhat those of the brain, and which sometimes contain a considerable quantity of serum.
In less degrees of this condition the cranial bones are more developed, the skull is less open, and the brain and its rnerubranes exhibit a greater degree of perfection. In all the ca.ses water is accumulated in the cerebral cavities. The following case quoted from Penchienati by Breschet in his article Anencephalie, in the Dictionnaire de Al6decine, illustrates the ap pearances in a by no means advanced stage of the deformity. The subject was a girl which
had lived three days. The corpora striata, optic thalami, were present with the hemi spheres. The lateral and third ventricles were greatly enlarged. The tubercula quadrigemina retaining their vesicular condition were likewise present, and also the pineal gland. These parts presented at the superior part of the cra nium a red eminence which was uncovered by the skin.
In some cases where the degree of openness of the cranium is reduced to a fissure, in front or behind, a tumour is found protruding, through either fissure, consisting of the brain, imper fectly developed, inclosed in its membranes. This condition is frequently combined with a greater or less extent of spina bifida.
The partial deficiencies of the brain itself are infinitely various. Those parts which are most frequently either altogether absent or im perfectly developed, are those which are not essential to the production of the organic vital phenomena. The coramissures are very fre quently wanting, the smaller ones oftener than the larger, such as the corpus adlosum and the pons Varolii. The hemispheres of the bram are frequently very imperfectly developed. The medulla oblongata and mesocepliale rarely exhibit any material imperfection.
In all cases of idiotcy there is a manifest imperfection in the developement of the brain. This is sufficiently plain to the most super ficial observer from the small size of the head which is so frequent a character of this state, and which is more especially remarkable in adult life, where the developetnent of the cm nium by no means keeps pace with that of the rest of the body.
As an example of the class of changes which take place in the brains of most idiots, I shall de scribe the appearances observed in the brain of an adult idiot which I examined in October, 1844.
On the upper surface of the brain the convo lutions svere not developed ; the surface of both hemispheres was perfectly smooth. The fissure of Sylvius was very deep and well marked, extending upwards and backwards ; at its po terior extremity there was a slight puckering indicating a feeble developernent of the insula of Reil.