Mental Diseases and Their Modern Treatment | Page 2

the core, explaining as we pass along, in brief, each part as we find it. This work has, I presume, already been performed by your professor of anatomy, and I shall merely enumerate the component parts of the head in this connection for the sole purpose of drawing your attention to a material structure as an organ of the mind, and then pass to a contemplation of the subtle processes of the mind itself.
The coverings of the brain are three in number:
1. The periostic (above the bone),--namely, the hair, scalp, and muscles. 2. The bony cranium. 3. The sub-osseous,--namely, the membranes lying beneath the skull and over the carebral mass.
The scalp is a thick, tough, tenacious covering, forming the base and ground-work whence springs that luxurious adornment, the human hair. The scalp is thicker than the skin of any other portion of the body. A thick scalp protects the brain from accidental injuries. It is also supposed to prevent a too rapid in-pouring of ideas upon the brain. The scalp is attached to the skull by means of the occipitofrontalis muscle. The latter covers the skull, and has attachments along the crest of the brow, over the eyes, and at the occiput, or back part of the head. It is by means of this muscle that the brows are elevated in token of surprise, or corrugated as an evidence of displeasure or chagrin. The occipitofrontalis muscle is thin even at its extremities or points of insertion. Over the top of the head it is but little more than a thick membrane or flattened tendon.
Beneath the scalp and its controlling muscle, we arrive at the skull, an egg-shaped, bony case, flattened underneath, the forepart of which gives attachments to the face. The skull is composed of flat bones consisting of two layers, an outer and an inner table, and a spongy tissue, known as diploe, between them. Where the walls are very thin there is but a single layer. The vault of the skull presents two minute openings (the parietal foramina) for the passage of small veins. At the base are many openings for the transmission of nerves, and for other purposes. The skull-cap proper is very strong, and built to resist heavy blows. The base of the skull is relatively weak and easily broken. The various bones of the skull are laced or inter-laced together by what are called the sutures in such a way as to oppose the tearing off of any bone by force acting in a single direction.
On removing the skull-cap we arrive at the three sub-osseous coverings called membranes. The first, or that next the skull, is termed the dura mater, which, as compared with the others, is thick and exceedingly tense and firm, resembling in some slight degree a drumhead or piece of parchment. Excepting on the crown, it is closely adherent to the skull, with which it is very intimately associated, as through its outward surfaces the minute vessels which supply the bony casing of the brain with blood find their way. The inner surface of the dura mater, that is, the surface next the brain, is smooth and oily, so to speak, thus relieving the slight friction which takes place between the brain and its protecting citadel, as the former swells into action under the pressure of excitement or subsides into a grateful calm during its appropriate periods for repose. The dura mater forms still another protection for the brain; its density and firmness resisting with vigor all encroachments from without, the splintered fragments of a fractured skull even being held in abeyance in many instances. By these appropriate means the most vital organ of the body is protected from fatal injuries.
The second membrane is termed the arachnoid from its supposed resemblance to a spider's web. It is a single layer of thin, delicate, connective tissue overhanging the convolutions of the brain, and dividing into two the spaces between the organ and the skull. The outer of these is called the subdural space, and the inner the subarachnoid. It was formerly supposed that the arachnoid membrane formed a close sac like the pleura, which envelops the lungs and lines the walls of the thorax, but investigations have tended to disprove this theory. What was supposed to be its outer, or reflected portion, is really one of the layers of the dura mater. The chief uses of the arachnoid seem to be to envelop and in some measure to protect the brain, and to secrete a fluid for the purpose of keeping it in a state best adapted for the proper performance of its functions.
The third membrane, which is discovered as we pursue our explorations, is termed the pia mater, or delicate mother. This, too, like the arachnoid, is a layer of connective tissue,