CHAP. XXVI.

OF MAN, HIS STRUCTURE AND FUNCTIONS.

General view of the human frame. Of the bones-Marrow--CartilageSynovia. Of the skeleton-The Head-Face; teeth, and bone in the tongue. The Trunk-Spine; pelvis, and thorax or chest; ribs, sternum. Superior Extremities-Shoulder; arm and hand. Inferior Extremities -Femur-Leg; patella, and foot. The muscles. Muscular motion. The brain and nerves.

IN contemplating the human structure-in developing its various functions-no attentive person can avoid beholding in a most striking manner, the wisdom and goodness of the Creator; to which, in fact, all knowledge and every system of education should lead.

From the superiority of his organization, Man, when compared with all other animated beings, may justly place himself at the head of the visible creation. His form is erect, his power is pre-eminent, and capable of bringing under his control the powers and perfections of all other creatures; his passions, given for the wisest purposes, are within the range of his own discipline; his happiness not confined to things of sense; his knowledge is progressive, and his duration is eternal. To his rank and station in the present world, this and the following

chapter will be devoted to his high expectations for futurity, the concluding pages of the work will be appropriated.

To understand the necessity and advantages of such a structure as that belonging to the human frame, we must consider what Man is, and what are the faculties with which he should be endowed. We must remember that the thinking part, or mind, is to be placed in a corporal fabric, to hold a correspondence with other material beings by the intervention of a body; hence the necessity of the brain, in which the mind, or thinking principle, dwells, as governor and superintendent of the whole fabric. As the mind is to correspond with the material beings which surround her, of course she must be supplied with organs fitted to receive the different kind of impressions that they will make. Hence she is provided with the organs of sense: the eye is adapted to receive impressions from light; the ear to those arising from sound; the nose is adapted to smelling, the mouth to tasting, and the skin to touching.

Again, the mind must be provided with organs of communication with the several parts of her own body, by means of the brain, fitted to convey her commands, and to have an influence over the whole. Hence nerves are given, which are a sort of cords that rise in the brain, and are dispersed in branches to every part of the body. They are intended to be the occasional monitors against all such impressions as might endanger the well being of the whole frame, or any particular part of it; which vindicates the Creator, in having subjected us to those disagreeable and painful sensations to which we are exposed in a thousand accidents of life.

The mind must likewise be endued with the power of moving its habitation, the corporal frame, from place to place; and accordingly she is furnished with limbs, and with muscles and tendons, which are the instruments of motion, and which by some unknown power, she has completely under her control.

To give stability, support, and shape to this fabric: to keep

the softer parts in their proper places, and for other important purposes, there must be some firm prop-work interwoven through the body. Such is the bony skeleton, with which we shall begin our description.

Of the Bones. The bones, constituting the basis and support of the body, are its most hard and solid parts: they are however organized like the other parts of the body, and like them supplied with blood by numerous vessels adapted to the purpose. Before birth, cartilage, a substance that will be explained hereafter, supplies the place of bones. And this cartilage is not afterwards hardened into bone, but is actually absorbed and carried away by one set of vessels, while another set is employed in depositing, in its room, matter for the formation of bone.

The bones are composed of a vascular substance, not differing materially in structure from the rest of the body, except that there is deposited in the interstices an earthy matter, which gives to the whole mass rigidity, strength, and a permanent figure.

According to the differences in their forms, bones are divided into the long and flat: and two kinds of structure may be observed in them in the one, the bony substance is condensed, and without interstices; in the other, there is a mere net-work of bony fibres and plates, leaving numerous intervals. This latter is denominated the cancellous substance of bones.

The cylindrical part of long bones is composed of the firmer substance, but the centre all the way through is left hollow, to contain a substance called marrow. In those extremities of bones which form the joints, to increase their surface there is a thin layer of the compact substance, but all the interior is cancellous. In broad flat bones, the firmer substance is formed into two plates or tables, and the interval between these is occupied by cancelli.

Many advantages arise from this arrangement, the long bones are made slender in the middle, to allow of the con

venient collocation of the large muscles around them: they become expanded at their extremities, to afford an extent of surface for the formation of joints, and the support of the body. The bones are hollow; for if all the earthy matter had been compacted in the smallest space by bringing its parts close together, they would have been such slender stems, as to be unsuitable to their offices; and if they had been of their present dimensions, and solid throughout, they would have been too weighty and unweildy. The bones possess nerves as well as arteries, veins, and absorbents, and though in their natural and healthy state they seem to be insensible, they become exquisitely sensible and painful when diseased.

Bones are covered by a strong and firm membrane, termed periosteum, on which the vessels are first distributed, and from this they descend into the substance of the bones.

The Marrow is an oily substance, secreted, or separated from the blood: its precise use is not yet ascertained, but it is known that the destruction of the marrow produces the death of the bone.

Bones are connected with each other by Ligaments, which are strong, white, flexible substances, and but little elastic: there are two kinds of ligaments, the round, or cord-like, which grow from the head of one bone, and are inserted into that of the other, tying the bones together; and the capsular ligament, which incloses the whole joint, as in a purse or bag, and which has numerous arteries opening upon its internal surface, for the purpose of keeping it moist, and of diminishing friction.

Cartilage is a semi-pellucid substance, which enters into the composition of several parts of the body: to preclude friction and concussion; all the bones, forming moveable joints, have their ends covered with plates of this cartilage; which being of a solid, smooth, elastic nature, renders the joints easy, and free from shocks in running, jumping, &c.

Synovia. Besides the fluid which the capsular ligament throws out, there are small fringe-like bodies placed within the

joints, for securing a constant supply of moisture. They secrete or separate a glairy and slippery liquor, called synovia, intended for lubricating the different surfaces of the joint. After the synovia has done its office, it is taken up into the mass of blood by the absorbent vessels, which arise by open extremities from all the cavities of the body.

OF THE SKELETON. The bones of an animal connected together after the soft paris are removed, is called a skeleton. The human skeleton is divided, for the purposes of description, into the head, the trunk, and the extremities. See the plate.

By the HEAD is meant all that spheroidal part which is placed above the first bone of the neck; it therefore compre→ hends the bones of the skull, and those of the face. The skull consists of eight bones, which form a vaulted cavity for lodging and defending the brain. These bones are composed of two plates or tables, and intermediate cancelli or latticework, nearly of the same structure and use, as that of other bones. The outer plate is the thicker and stronger of the two, for the purpose of warding off external injuries from the head. The bones of the skull are joined together by sutures, which are indented or dove-tailed seams. The bones of the skull ossify from the centre towards the circumference, their fibres spreading and extending on every side; till at length the different bones meet, and shooting in between each other, form the suture or serrated line. In this way Nature, in the formation of all the bones, hastens their ossification, by beginning the process in many points at once; and she observes the same law in healing or uniting a broken bone, as well as in forming the skull.

The face is the irregular pile of bones composing the fore and under part of the head. It constitutes the bony portion of some of the organs of sense; affording sockets for the eyes, an arch to the nose, and a support to the palate: it forms the basis of human physiognomy. It is usually divided into the upper and lower jaws: the former consists of six bones on each side, and of one in the middle, and of sixteen teeth.