The Ribs.—The ribs may be compared to the girders of a building; though they look more like the hoops

of a cask, than like girders. There are twelve on either side. Each of them is connected, by one of its ends, to the large post or spine; and by the other to a short post in front-the breast-bone. Only seven, however, are joined closely to the breast-bone itself. This junction is effected by means of cartilages, to allow of greater freedom of motion in the chest, so essential to full respiration, and vigorous circulation of the blood. These cartilages are shown in the plate, by fainter lines than those which represent the bony portions of the ribs.

The other five go only a part of the way across, and then unite with the cartilages of the upper seven. Those ribs which are continued round from the spine, and join with the breast-bone, are called true ribs; the others, which do not form this attachment, are called false ribs. On the preceding page is a view of this part of the frame.

The length of the ribs increases from the first or upper one, till you come to the seventh, which is the longest. From the seventh to the twelfth, they grow shorter again, and the cartilages of course, become longer in the same proportion. The twelfth rib is very short indeed.

The number of ribs is almost always twelve; but sometimes there are only eleven, and at others thirteen. But instances of more or less than twelve, hardly occur in one person in a thousand.

In the old bygone days of ignorance and superstition, a notion prevailed, which is not yet entirely extinct, that the man has one rib less on one side than on the other. It was said, that as Eve was formed of a rib taken from Adam's side, he and all his male posterity have one rib the less for it. I hardly need say that this notion is wholly unfounded.

Breast-bone.—I have just alluded to the breast-bone. The name of this in books, is the sternum. It is usually considered as only one bone; but, like many others of the human frame, in infancy and in youth, it consists of several pieces (usually three in number), closely united by gristle, or cartilage, but in advanced life, the whole generally becomes one solid bone. Long-continued boiling, however, will separate almost any of the bones, which are formed in this manner.

Braces.-There are a few other parts of the frame of

the second story, which remain to be noticed, and which They are four in number-two They are

I shall call the braces. before, and two behind.

1. The Collar-bone.-This forms a kind of brace between the shoulder and the breast-bone, and so nearly resembles a rib, that a separate cut, to show its shape and position, seems unnecessary. You will see it in two or three of the engravings, running across from the shoulder, to the breast-bone or sternum. It keeps the shoulder at a proper distance from the thorax, or bony cavity of the chest; and serves as an attachment to several muscles.

2. The Shoulder-blade.-This is a broad, flat bone, with ridges on it, for the attachment of muscles; and, at the fore part, is the hollow or socket, in which the round head or ball

of the humerus, or arm-bone, lies and moves. Here is a view of it behind.

This bone is called by anatomists the scapula, and serves as a broad attachment to several large muscles, which assist in moving the arms freely, in every

direction, as well as affording aid in respiration.

CHAPTER VI.

BODY OF THE HOUSE-continued,

Arms. These are not posts, for in their natural position, they support nothing. They are not braces, for they strengthen no part of the frame. They are properly appendages, but they are very convenient ones; and though they can be removed without spoiling the building, their loss very much injures it. They seem to answer, in a great degree, the purposes of stairs, ladders, tackles, pulleys, and other machinery for raising things from the ground or elsewhere, and conveying them to the upper part of the building. These appendages,— we may as well at once call them the arms and hands,— answer, however, a much better purpose than any of these simply mechanical contrivances.

The arm and hand, taken together, constitute a most wonderful apparatus for motion. The particular structure of the joints, as well as the peculiarities of the hand, must be reserved for another place; but it is necessary here, to say a little about the arm.

The bones of the arm have a general resemblance to those of the leg. The upper part consists of only one bone. This is long and round, and is called the humerus. It is fastened above to the scapula; below, at the elbow, it is connected to the two bones of the lower half of the arm by a joint like a hinge, and by ligaments, or straps, which extend from near the lower end of the upper bone, to the topmost end of the others. The largest of the two latter bones is called the ulna, which is a Latin word for cubit, because the arm, below the elbow, is usually considered to be about a cubit in length. The smaller

one is called the radius, or spoke, from its supposed resemblance to the spoke of a wheel. It is the bone from the elbow, on a line with the thumb.

The connexion at the shoulder is such, that the arm can be moved in almost every conceivable direction. The elbow joint only admits of one sort of motion, namely, forward and backward, like a door on its hinges. But the connexion of the radius, or smaller bone of the arm, with the ulna, or larger one, is such, that it more than makes up this deficiency. The upper end of the radius, having a rotatory motion in a depression of the ulna, allows the hand to be placed with each of its surfaces upwards, with equal facility. These motions arè usually designated by the terms pronation, when the palm of the hand is downwards, and supination, when the palm of the hand is upwards. Then the wrist, consisting as it does of eight bones, all moveable, and being so connected with the lower bones of the arm, as to admit of very free motion, renders the arm one of the most useful contrivances in the world. It will perform movements as various and as rapid as the trunk of the elephant; and would, probably, if it were not so common, excite as much surprise.

It was said, that this whole member could be torn off without spoiling the building. Cheselden, an eminent anatomist, relates that a miller had the whole arm, shoulder-blade and all, torn off, and yet his life was not injured. The great danger, in such cases, is from bleeding; but torn blood-vessels do not bleed so freely as those which are cut.

The Hand.—I wish to give you a few particulars about the hand. This extremity of the arm is by far the most curious part of it. Indeed, I do not know that