tion is carried to some depth in the brain, the lateral ventricles are opened by their anterior extremities, each of these extremities terminating in a cul-de-sac, answering to a frontal eminence. In the interval between these two cul-de-sacs of the anterior extremities of the ventricles we reach the anterior curve of the corpus callosum. If we saw in the same way the two superior occipital protuberances, we arrive at the posterior extremity of the two lateral ventricles, each of these extremities ending in a hollow cone, answering to one of the superior occipital depressions and eminences. Lastly, if the saw is made to divide the two parietal eminences at their summits, and that portion of the long vault intermediate between them, it leads to that part of the lateral ventricles which is the most spacious and projects the most outwards. It is in this part of the ventricles that is situated, so to speak, the confluence of the anterior, posterior, and temporal regions of these cavities. The same section which leads from the parietal eminences to that part of the lateral ventricles which is the most spacious and projects the most outwards, falls in the interval of the two eminences and of the corresponding portion of the ventricles upon the posterior margin of the corpus callosum.

There exists on a level with the squamous portion of the temporal bone a depression in the interior of the cranium and a corresponding eminence, almost as considerable, on the outside. If we cut through this eminence and the contiguous part of the brain at the same time, we open the base of the temporal region of the ventricle.

Now as there is nothing on the surface of the brain to account for the cranial prominences of which I have just spoken, it appears to me that we may very fairly consider them as caused by the shape of the corresponding regions of the ventricles. This conclusion is strengthened by comparing the form of these eminences with that of the portions of the ventricles corresponding to them. The frontal eminences are round, like the two cul-de-sacs forming the anterior extremities of the ventricles. The occipital protuberances, and especially the depressions answering to them in the interior of the skull, are sharper, if this language is applicable to protuberances and depressions; and the greater acuteness of the posterior extremities of the ventricles in relation with these protuberances, is a fact sufficiently notorious. Lastly, the temporal eminences are oblique in the same direction as the corresponding part of the hollow of the ventricles. But the influence of the ventricular cavities, or of the serous sacs of the brain, is not confined to the formation of the different

pairs of eminences which I have just pointed out;it extends also to the form of the skull in general, which, in fact, it contributes to determine.

The different transverse sections, which I have supposed to be made on a level with the centre of all these pairs of eminences on the median zone of the cranial vault, divide this me-dian zone into four regions, always perceptible during life, and each of them presenting an angular curve on the transverse line which separates it from the neighbouring regions. All of them display too an agreement in form and proportions with the corresponding region of the envelope of the ventricles, which seems to me incontestable.

The first region, comprised between the frontal eminences and the inferior boundary of the forehead, answers exclusively to the convolutions developed in front of and beneath the corpus callosum, and presents but a small projection from above downwards, like the corresponding part of the ventricles. The lower projection on this part of the forehead does not always indicate a considerable development of the corresponding part of the brain. It may, in fact, be simply owing to the great size of the frontal eminences, and in this case the fact may be ascertained by percussion.

The second region, included between the frontal and parietal eminences, always forms the largest division of the median zone of the cranial vault; it is arched like the corpus callosum itself, and corresponds to the convolutions above this body. Its size, compared with that of the other regions of the bony arch, bears the same proportion to theirs, that the extent of the superior part of the corpus callosum does to the other fibrous parts enveloping the serous cavities of the brain.

A considerable eminence is very often seen on the median line towards the centre of this region, in the upper part of the os frontis. This also appears to me, like all the other projections on the median line, to be owing to a thickening of the bones.

The third region, intermediate between the transverse section of the parietal eminences and the superior occipital protuberances, is scarcely ever convex longitudinally. It is mostly straight or concave in this direction. Frequently even it presents on the median line a well-marked fossa. The complete separation for the two hemispheres at this part, the absence of the corpus callosum, lifted up as in the others by the fluid of the ventricles, and the superior concavity observed in passing from those parts of the ventricles covered by the corpus callosum, to those formed by a distinct fibrous cone in each posterior half of the hemispheres, are in accordance with these peculiarities. To this region correspond the convolutions situated behind the posterior margin of the corpus callosum as far as the posterior termination of the ventricles.

Lastly, the fourth region, situated in the interval between the superior occipital protuberances and the upper curved line of the occiput, divides the latter into a median convex quadrangle, and two lateral triangles, whose pointed summits terminate near the mastoid process. Now these triangles, instead of being convex like the rest of the median arch, almost always present a plain or even concave surface. The depressed portions of these triangles correspond at their sharp summits to the insertion of the tentorium cerebelli and the external part of the lambdoidal suture.

In the temporal regions of the cranial arch, we always remark, on a level with the great wing of the sphenoid bone, a depression running upwards and backwards in the same direction as the fissure of Sylvius, to which it corresponds. A right line drawn from the top of this depression towards the centre of the parietal eminence, marks the course of the fissure of Sylvius, and allows us to measure, on the living subject, the comparative volume of cerebral substance situated in front, and of that behind, this fissure.

Now the fissure of Sylvius, and the cranial depression answering to it at the fore part of the temporal fossa, are variously modified according to the modifications of the ventricular hollow. The anterior and temporal regions of these cavities are separated by a large nervous mass which follows the crus cerebri. The fore part of the ventricle is enlarged above this mass and the temporal part of the ventricle below it.

The fissure of Sylvius, then, forms the interval between two regions of the ventricle, the frontal and the temporal, and consequently the interval between the convolutions covering in these two distinct regions of the serous cavity. It ceases above, at the part where these regions of the ventricular cavity unite into a common conflux. Its deepest part is below, at the bottom of the widest interval between the frontal and temporal extremities of the ventricle.

Thus the form of the brain, and that of the skull also, would seem to be determined in their general character by the form of the serous sacs inclosed in the hemispheres, and constantly filled with the fluid peculiar to them.

This is not meant to imply that the cerebral convolutions do not exert any influence on the secondary shape of the

skull. So far from that, observation proves that when the convolutions are greatly developed, the skull, though retaining the form that we have assigned to it, swells out in the intervening regions between the eminences corresponding to the extremities of the ventricles, so as almost to obliterate them; or if they still remain very prominent, they acquire a very great diameter. In this case, the head, modified by the development of the convolutions, acquires the cerebral forın, par excellence.

On the contrary, when the convolutions are but very little developed, the prominences, and the regions separating them, are all exceedingly well marked, whilst, at the same time the projections corresponding to the ventricular extremities have a very small diameter. The head then assumes, if I may be allowed to use such a term, the peculiarly ventricular form.

The relations just now pointed out between the projecting points of the skull and the corresponding regions of the ventricles, appear still further confirmed by observing what takes place in chronic hydrocephalus. One of the first symptoms of this dropsy of the ventricles is the increased salience of these cranial tumours. But I shall not pursue the details of the relations between the skull and the brain any further at present. I consider them useful in reference to what is called surgical anatomy, and also for all those cases which call for an exact knowledge of the relations between the skull and the brain. The subject has been pursued in a work of some extent, which I intend before long to lay before the public.

To sum up, I consider that the fibrous parts of the brain are conductors; some from without to within, others from within to without. I believe that these conducting parts may be distinguished into afferentes and efferentes, and that the distinct course of both the one and the other may be demonstrated. The first are inserted especially into the circumference of the gray substance, and the second into its internal surface.

The gray substance of the convolutions intermediate between the two preceding orders of fibrous parts, seems to me to be the material substratum, through the instrumentality of which the will directs the movements of the body.

The prominences constantly seen coupled in pairs on the arch of the skull appear to me to be produced by the projection of the corresponding regions of the ventricles. The median eminences, not universally present, appear to be produced by a thickening of the bones.

The median zone of the cranial arch is naturally divided into four sections; one, anterior, corresponding to the fore part of the corpus callosum, and to the convolutions developed before and beneath the level of the same part of that body.

The second, more extensive, intermediate between the frontal and parietal eminences, is of a length proportioned to the extent from before to behind of the corpus callosum. It ceases behind on a level with the posterior margin of that body.

The third section, often concave from above to below, sometimes even hollowed into a furrow on the median line, is proportionate in length to that of that part of the hemispheres completely separated, behind the corpus callosum.

The fourth section, intermediate between the superior occipital protuberances and the upper curved line of the os occipitis, displays in its middle a projecting quadrangle, corresponding to the hinder extremities of the ventricles, and to the convolutions situated behind and beneath these extremities *.

March 30, 1840.

V. Remarks on the permanent Soap Film and on Thin Plates. By JOSEPH READE, M.D.

"Scilicet ut possem curvo dignoscere rectum,

Atque inter silvas Academi quærere verum."-HORACE.

To the Editors of the Philosophical Magazine and Journal. GENTLEMEN,

AS the entire of the second book of Newton's Optics is based on the theory first advanced by Dr. Hook, or rather by Mr. Boyle, "that colours are produced by the thicknesses of the plates," supposing your scientific readers well acquainted with that great philosopher's experiments, I shall immediately proceed with my own. Should these be capable of explanation according to the Newtonian theory, I shall be ever ready to alter my opinions, and what at present I conceive to be legitimate inferences. Aware of the difficulties I have to encounter, and of the prejudices against everything opposed to a doctrine stamped with the name of Newton, and advocated by the most celebrated characters, I hope for the indulgence of my scientific readers.

Experiment 1. Having made a permanent soap film, as already described in your Journal†, and shown two years ago at the British Association at Liverpool, I placed the bottle on an inclined plane on the table until all the bands of colours

* An able report on the subject of Dr. Foville's researches has recently been presented to the Academy of Sciences by Professor Blainville. It contains further discoveries made by the Doctor with regard to the origin of the eighth pair of nerves.

† (Lond. and Ed. Phil. Mag. vol. xi. p. 375.-EDIT.]