and blood-vessels and bone all together; and, if you look again, you will see that between them there is a delicate stringy substance which binds and packs them all together, just as cotton-wool is used to pack up delicate toys and instruments. This stringy packing material which you have torn and spoilt is called connective because it connects all the parts together.

Well, then, in the leg (and it is just the same in the arm) we have skin, fat, muscle, tendons, blood-vessels, nerves, and bone all packed together with connective and covered with skin. These together form the solid leg. We may speak of them as the tissues of the leg.

2. THORAX AND ABDOMEN.

If now you turn to the trunk and cut through the skin of the belly, you will first of all see muscles again, with nerves and blood-vessels as before. But when you carefully cut through the muscles (for you cannot easily separate them from each other here), you come upon something which you did not find in the leg, a great cavity. This is something quite new

there is nothing like it in the leg-a great cavity, quite filled with something, but still a great cavity; and if you slit the rabbit right up the front of its trunk and turn down or cut away the sides as has been done in Fig. 1, you will see that the whole trunk is hollow from top to bottom, from the neck to the legs.

If you look carefully, you will see that the cavity is divided into two by a cross partition (Fig. 1, B) called

FIG. 1.-The Viscera of a Rabbit as seen upon simply opening the cavities of the Thorax and Abdomen without any further dissection.

A, cavity of the thorax, pleural cavity of either side; B, diaphragm; C, ventricles of the heart; D, auricles; E, pulmonary artery; F, aorta; G, lungs collapsed, and occupying only the back part of the chest; H, lateral portions of pleural membranes; I, cartilage at the end of sternum; K, portion of the wall of body left between thorax and abdomen; a, cut ends of the ribs; L, the liver, in this case lying more to the left than the right of the body; M, the stomach; N, duodenum; 0, small intestine; P, the cæcum, so largely developed in this and other herbivorous animals; Q, the large intestine.

the diaphragm. The part below the diaphragm is the larger of the two, and is called the abdomen or belly; in it you will see a large dark red mass, which is the liver (L). Near the liver is the smooth pale stomach (M), and filling up the rest of the abdomen you will see the coils of the intestine or bowel, very narrow in some parts (0), very broad (PQ), broader even than the stomach, in others. If you pull the bowels on one side, as you easily can do, you will find lying underneath them two small brownish red lumps, one on each side. These are the kidneys.

In the smaller cavity above the diaphragm, called the thorax or chest, you will see in the middle the heart (C), and on each side of the heart two pink bodies, which when you squeeze them feel spongy. These are the two lungs (G). You will notice that the heart and lungs do not fill up the cavity of the chest nearly so much as the liver, stomach, bowels, &c., fill up the cavity of the belly. In fact, in the chest there seems to be a large empty space. But, in truth, the lungs did quite fill the chest before you opened it, but shrank up very much directly you cut into it, and so left the great space you see.

3. THE VERTEBRAL COLUMN.

The trunk then is really a great chamber containing what are called the viscera, and divided into an upper and lower half, the upper half being filled with the heart and lungs, the lower with the liver, stomach,

never keep

Some part

And indeed

bowels, and some other organs. In front the abdomen is covered by skin and muscle only. But if all the sides of the trunk were made of such soft material it would be then a mere bag which could its shape unless it were stuffed quite full. of it must be strengthened and stiffened. the trunk is not a bag with soft yielding sides, but a box with walls which are in part firm and hard. You noticed that, when you were cutting through the front of the chest, you had to cut through several hard places. These were the ribs (Fig. 1, a), made either of hard bone or of a softer gristly substance called cartilage. And if you take away all the viscera from the cavity of the trunk and pass your finger along the back of the cavity, you will feel all the way down from the neck to the legs a hard part. This is the backbone or vertebral column. When you want to make a straw man stand upright you run a pole right through him to give him support. Such a support is the backbone to your own body, keeping the trunk from falling together.

In the abdomen nothing more is wanted than this backbone, the sides and front of the cavity being covered in with skin and muscle only. In the chest the sides are strengthened by the ribs, long thin hoops of bone which are fastened to the backbone behind and meet in front in a firm hard part, partly bone, partly cartilage, called the sternum.

But this backbone is not made of one long straight piece of bone. If it were, you would never be able

That The solid bung is what hollow ring is what is

to bend your body. To enable you to do this, it is made up of ever so many little flat round pieces of bone, laid one a-top of the other, with their flat sides carefully joined together, like so many bungs stuck together. Each of these little round flat pieces of the backbone is called a vertebra, and is of a very peculiar shape. Suppose you took a bung of bone, and fastened on to one side of its edge a ring of bone. would represent a vertebra. is called the body, and the called the arch of the vertebra. Now if you put a number of these bodies together one upon the top of the other, so that the bodies all came together and the rings all came together, you would have something very like the vertebral column (see Fig. 2). The bungs or bodies would make a solid jointed pillar, and the rings or arches would make together a tunnel or canal. And that is really what you have in the backbone. Only each vertebra is not exactly shaped like a bung and a ring; the body is very like a bung, but the arch is rough and jagged, and the bodies are joined together in a particular way. Still we have all the bodies of the vertebræ forming together a solid pillar which gives support to the trunk; and the arches forming together a tunnel or canal which is called the spinal canal (Fig. 2, C.S.), the use of which we shall see directly. The round flat body of each vertebra is turned to the front towards the cavity of the trunk, and it is the row of vertebral bodies which you feel as a hard ridge when you pass your fingers down

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