"Numberless experiments prove, that the nerves are necessary to life; and that when the brain, or medulla spinalis, is much injured, life is at an end, or at least health: yet no part of the brain being injured, immediate death may ensue from different causes, though an injury of the medulla oblongata is so instantly fatal.
"Two glands are said to be in the brain, viz. the su-perior or glandula pinealis; and the inferior or glandula pituitaria, which see. They have the external appearance of glands, but as to their being such is not certainly known.
"The cerebrum fills all the upper portion of the cavity of the cranium, or the portion which lies above the transverse septum; each lateral half is divided into three eminences, called lobes; one anterior, one middle, and one posterior.
"The blood vessels which supply the cerebrum, cerebellum, and medulla oblongata, come partly from the carotid, and partly from the vertebral, arteries. The veins of the cerebrum and cerebellum may, in general, be looked on as branches not only of the longitudinal sinus of the dura mater, and of the two great lateral sinuses, but also of all the inferior sinuses of this membrane, in all which the veins terminate by different trunks."
"Plain truth,"it is observed, "needs no flowers of speech,"and we long hesitated whether this simple, this bald, unornamented description might not pass as plain sound science. If we could only add to it speculation, yet when this is the mode, a dictionary, which is to give the very body of the time its form and pressure, must admit of speculation. As the room it employed was but small, and as it contained a text which might prevent repetition, we have, therefore, preserved it, and shall add the commentary.
A brain is the distinction of the more perfect animals, and its proportional bulk is the criterion of more perfect intellectual faculties. With a diminished brain, animals dwindle in the scale of intellect; and Camper's facial line, which marks the varying boundary between the most perfect human form and the meanest animal which possesses this distinguishing organ, depends on the bulk of the cerebrum. This is the part originally created; and the integuments, whether bony or membranous, are adapted to its primordial shape.
When the head is opened, and the tense dura mater removed (vide in verbo), we perceive a bluish white mass, formed apparently of vermicular convolutions, variegated with vessels of a deeper blue. This mass is divided into two hemispheres, which fill the upper part of the head, and form the projection of the forehead. Between the hemispheres passes a membrane, called the falx; because, when separated, it resembles a scythe or reaping hook; and these are united below the falx by a white substance, firmer than the brain, which has been just styled corpus callosum. This hard substance is continued downwards, and divides two ventricles; but as it is there thinner, it has obtained the name of septum lucidum. This corpus callosum, continued backward, connects the cerebrum and cerebellum; and as when cut through in a horizontal direction it appears of an oval shape, it has been called the centrum ovale.
When the base of a skull is examined, it appears to have numerous projections and depressions, adapted to the cavities or reliefs of the brain which rests on it. Behind are two spherical cavities, which contain the cerebellum; and between them is a hole, through which the medulla spinalis passes out, or, according to modern speculators, enters. We need not enlarge furtheron these projections, as our predecessors have given their appellations, except to add, that the pineal gland seated in the midst, on a kind of throne, the sella turcica of the sphenoidal bone, the only part to which no other corresponds, has been styled the seat of the soul. Less eccentric observers have supposed it to be a conglobate gland; but as we have found it the seat of calculous concretions, we must consider it as a secretory organ, whatever fluid it may furnish. To this subject, however, we shall return.
When the brain is examined more nearly we find a very thin membrane, called the pia mater, which accompanies the convolutions, and sinks into the interstices. This membrane, which will be afterwards described, conveys the blood vessels to the cineritious part of the cerebrum, and is itself covered with a cobweb-like membrane, which, however, does not follow it into the sulci, called tunica arachnoides. When we cut into the substance of the brain, we shall find for a little space within a brown substance, called, without any strict accuracy, the cineritious portion; which follows all the sulci of the convolutions, terminating in lines or rounded points, as directed by these. To this portion the medulla is united, and neither encroach on the other, but in the angles of the sulci: the depth of the cineritious portion is generally uniform. The colour is derived from very minute blood vessels; for, strictly speaking, the medullary part suffers vessels only to pass through it. Those apparently dispersed on it, form such conspicuous streaks, as prevent us from thinking that the medulla contributes any thing further than a support: there is certainly no such minute distribution as generally attends any glandular apparatus, or distinguishes any organ destined for an important purpose.
This cineritious portion is certainly designed for an office of the greatest consequence; for we shall find that whatever be the proportion of the brain, it is al-wavs present, and by no means in the ratio of the medulla; and in parts where seemingly additional nervous power is required, in the course of the nerves, adventitious ash coloured matter is observed. In the substance of the brain, striae of a cineritious hue are found; and some projections wholly consist of it, with different tints, while others contain this matter surrounded with, instead of containing, the medullary substance.