ly indicates that extent of surface is highly important to its functions. In certain low classes of the inferior animals, there are no convolutions. As we ascend in the scale of beings, they increase," and in man above all other animals, are the convolutions numerous, and the sulci (or furrows) deep, and, consequently, the cineritious mass great, and its extension of surface far beyond that of all other creatures."-Bell's Anat. ii. 386.

The cineritious matter is extended over all the upper, lateral, and over part of the inferior surfaces of the brain: the white or medullary matter lies within it, and in some places in intimate combination with it. Medullary fibres run from the convolutions of the brain upon one side to the convolutions on the other. These are called commissures. "Unless," says Mr BELL," the cineritious masses were important organs, why should there be commissures or nerves forming a distinct system, arising and terminating in nothing? But if we take them as commissures, i. e. bonds of union betwixt the corresponding sides of the great organ of the mind, we at once perceive how careful nature is to unite the two lateral organs together, and out of two organs to make ONE MORE PERFECT.”—P. 386.

Each side of the brain, and also the cerebellum, are supplied with separate arteries conveying the blood to them; but the sinuses or canals, by means of which the blood is returned to the heart, are common to them all.

The CEREBELLUM is composed of the same nervous matter with the brain, and presents both cineritious and medullary matter; but, in form and internal arrangement, it is quite unlike the brain. The cerebellum is separated from the brain by a strong membrane, called the tentorium: in animals which leap, as the cat and tiger, the separation is produced by a thin plate of bone. Its fibres, however, originate in that part of the medulla oblongata called the corpora restiformia, from which also the organs of several feelings or propensities arise; so that the brain and cere

bellum, although separated by the tentorium, are both connected with the medulla oblongata, and through it with each other.

The MEDULLA OBLONGATA is sometimes spoken of as one of the three great divisions of the brain. It is, in fact, the part from which the fibrous matter of the brain and cerebellum proceeds, and it forms, as it were, the capital of the column of the spinal marrow.

OF THE INTEGUMENTS OF THE BRAIN.

! THE brain is formed before the bones which invest it. The ossification of the bones of the skull is a gradual process. The brain already formed is invested with strong membranes, and betwixt the coats of the outer membrane the points of ossification commence, which process is not completed until the ninth year.

During life, the brain is embraced in its whole peripheral extent by a very thin transparent and delicate membrane called the pia mater, which sinks down into its furrows, and serves to convey the blood vessels to its different parts. Immediately above the pia mater, is an extremely thin membrane, named the tunica arachnoidea, on account of its extreme tenuity, resembling a spider's web. It covers the surface of the brain uniformly without passing into its folds or cavities. It secretes matter, to lubricate the surfaces of the pia and dura mater. The dura mater is also a thin but strong opaque membrane lining and strongly adhering to the inner surface of the skull, and which embraces the outer surface of the brain above the membrane last mentioned. When in health it does not possess sensibility, and has been pricked without causing pain. All these membranes are pliant in the highest degree, and accommodate themselves precisely to the figure of

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the brain. The brain, enclosed in them, fills exactly the interior of the skull; so that a cast, in plaster, of the interior of the skull, is a fac simile of the brain, covered by the dura mater. Between the dura mater and brain a very small quantity of fluid is said to exist; but not exceeding a line in thickness. This fluid does not, in any degree that can be distinguished by the hand or eye, cause the form of the interior of the skull to differ from the form of the exterior of the brain enveloped by the dura mater. The skull is not an adamantine barrier, confining the brain within specific boundaries; but a strong, yet yielding covering, shielding it, and accommodating itself to its size, while in the progress of its growth. It resembles, in this respect, the shell of a crab or of a snail. At birth, it is small; it increases as the brain increases; and it stops in development, when the brain has attained its full size. A process of absorption and deposition goes continually on in its substance; so that, if the brain presses from within, the renovating particles arrange themselves according to this pressure, and thus the figure of the skull and of the brain in general correspond. The figures represent the skull at

birth and at maturity respectively.

AA sutures. B mastoid process or bony projection behind the ear.

C process of the occipital spine.

The skull is composed of eight bones, for the most part joined by indented edges (AA in figures p. 77), like dovetailing in carpenter-work. The lines of junction are named Sutures *.

This figure represents the two sides of the skull cut away, down nearly to the level of the eyebrow, leaving a narrow ridge in the middle of the top standing. AAA is the edge of the skull, resembling an arch. The outer surface is called the outer table, the inner surface the inner table; the fine waving lines or net-work between them, like cells in a marrow-bone, is the diploë. The substance hanging down from the skull, having delicate lines traced on it, like the sap-vessels in leaves, is the membrane which separates the two halves of the brain. It is called the falciform process of the dura mater, from its resemblance to a scythe. The lines are the bloodvessels; the blood returning from the brain to the heart, goes up these vessels into a canal formed by the membrane all along the line of its attachment to the skull. The course of the blood through the canal is from the front backwards, and then downwards. The two hemispheres of the brain are completely separated, as far as this membrane extends in the cut: At the lower edge of it a white space appears, and the commissure, or collection of fibres which unites the two sides, goes through that space. The cerebellum lies at C, in a part of the skull not opened. The membrane, on reaching the point at C, spreads out to the right and left, and runs forward, and separates the cerebellum from the brain; the brain lying above, and the cerebellum below it. B is the mastoid process, or bone to which the mastoid muscles of the neck are attached. It lies immediately behind the opening of the ear, and is not connected with the brain.

• Mr LUKE O'NEILL sells a cast of the skull, accompanied by an explanatory card, pointing out all the bones, sutures, and processes, with their names; which will render the subject more intelligible than any description.

of the skull, are called their external and internal tables, or plates, to distinguish them from the intermediate part called the diploë, which is of a looser and somewhat cellular texture, resembling the internal structure of the bones. As the diploë is nearly equally thick in every part, it follows that the two tables of the skull are nearly parallel to each other. The internal, indeed, bears some slight impressions of blood vessels, glands, &c., which do not appear externally, but these are so small as not to interfere with phrenological observations. The departure from perfect parallelism, where it occurs, is limited to a line,th or fth of an inch, according to the age and health of the individual. The difference in development between a large and a small organ of the propensities and some of the sentiments, amounts to an inch and upwards; and to a quarter of an inch in the organs of intellect, which are naturally smaller than the others.

The integuments which cover the skull on the outside, indisputably lie close upon its surface, and are so completely parallel, as to exhibit its true figure. Thus, then, there is no obstacle in general to the discovery of the figure of the brain, by observations on the form of the skull.

This doctrine has been disputed by many opponents of phrenology; but the greatest anatomists have taught it. MAGENDIE, in his Compendium of Physiology, says, that "the only way of estimating the volume of the brain in a living person, is to measure the dimensions of the skull; every other means, even that proposed by Camper, is uncertain." -Milligan's Translation, p. 104.

Mr CHARLES BELL also observes, "Thus, we find that the bones of the head are moulded to the brain, and the peculiar shapes of the bones of the head are determined by the original peculiarity in the shape of the brain *. Dr GORDon, also,

• Bell's Anat. ii. 390. Mr BELL adds in foot note, "Certainly the skull is adapted to the form of the brain, but there is a deeper question, which our craniologists have forgotten,-Is the brain constituted in shape with a reference to the future form of the head ?” It is difficult to see the