Obrázky na stránke
PDF
ePub

CHAP. V.

OF CRANIOLOGY AND CRANIOSCOPY.

BUT the living brain can never be exposed to observation; and from the nature of its substance, loses much of its form and texture soon after the death of the subject.

The inference therefore of the physiologist concerning the organs of the brain would avail him but little, unless some certain connection were ascertained between the brain and its permanent covering, the skull. - This connection is asserted in the following fundainental position

" That the internal lamina or plate of the brain-pan or skull is, during the life of man,

perpetually formed by the brain itself: And " that therefore where the internal and erternal

plates of the skull run parallel, we may inser " the form of the brain from the outward " shape of the skull." E 2

On

[ocr errors]
[ocr errors]

On this fact, and on that before stated, that each of the circumvolutions of the cerebrum consists of an organ of some intellectual or sensible power, the greater size and developement of which would of course give the skull its peculiar shape, rest the sciences of craniology and cranioscopy. The one of which asserts that the shape of the skull gives the law, by which, not the actual character, but the tendencies and dispositions towards character in men, are determined ; and the other ásserts, that that law can be discerned and ascertained by contemplating the shape of the skull.

The merely observing the process of ossification, is sufficient to suggest, that the bone is essentially the passive result of the more active and finely organised matter to which it is attached ; and this is further confirmed by its subsequent diminution, and the mode of its being affected by the diseases of the brain. When the brain, with its three coats or skins, the pia mater, tunica arachnoides, and dura mater, which attend it in its circumvolutions, is already perfectly formed, there forms itself on eight parts of the external skin, a point of ossification, at which a slimy matter exudes; this hardens, lines diverge from it in every direction, and at length the eight bones of

the

the skull are formed; these lines of concretion firmly attach themselves to the dura mater, they harden, meet at the sutures or seams, and complete, after the birth, the covering of the skull.

The best commentary upon, and deductions from this statement, will consist in answering the objections made to the general theory

1.) Can we infer the form of the internal plate of the skull, from that of the external plate ? Answer: The lamina run parallel till the individual is about forty years of age, later in life variations take place, as well through age as disease, which will be noticed; and the

power of inferring the one from the other suffers restriction.

2.) As the brain is of so soft, almost fluid a substance; is it found that the organs retain the same place in the brain, so that they can be with certainty recognised ? Answer. Observation shews that the folds and circuinvolutions of the cerebrum, in the more simple animals, are quite symmetrical; and in man, nearly so. And tho' the extent and boundaries of the organs may not yet be always determined, their relative position and their relative perfection may be ascertained. E 3

3.) is

3.) Is it not more probable that the form of the skull being determined at the birth, fixes that of the brain ?

On no account; for whatever violence may be done to the bones of the skull during the birth, those bones return into their natural state, partly from their elasticity, partly from the active power of the brain working outwards. It is only when the bone is broken, and the brain itself is injured, that the intellect is affected, and that the skull retains the form which violence had impressed on it.

Gall produced, in confirmation of this statement, the remarkable skull of a man full grown, which was at the birth broken by Levret's forceps on both sides, and never recovered its form. The mark of the forceps was distinctly observed on the outside; but the internal lamella had no impression upon it, because not being broken, the power of the brain had restored it to its original shape. Yet from the thinness of the internal lamella, and the violence with which the forceps forced in the outer lamella, it having, by touching the inner lamella, destroyed the dipploe between, it cannot be doubted that some vio, lence must have been done also to the inner plate.

The

The principal cause of this activity of the brain operating outwards, lies in the regular motion of the brain occasioned by the circulation of the blood : this is the reason why swellings and aneurismata in the membranes of the brain 'never work inwards but outwards; that in case of wounds

upon

the skull, the mass of the brain presses outwards; that the vessels of the brain and its coats press upon the internal lamina of the bone. And this is in like manner the reason why, when at the birth, the bones of the skull are pressed or pushed wrong, without being broken, the brain under the place suffering violence, instead of being paralysed and destroyed, recovers itself by its own energy, remedies the injury, and forces the

parts

into their proper place. How otherwise do the heads of animals recover their shape, which are often pressed in during the birth ?

4.) But are not the most important organs of animal life and of the intellectual functions, formed after the birth, and long after the skull is completely formed ? It is ascertained that certain organs are formed after the birth, and G. himself asserts that the brain alters its shape in conformity with such subsequent formation.

It

« PredošláPokračovať »