Now try to put back everything in its place, and you will find that though you have neither cut nor torn nor broken either muscle or blood-vessel or bone, you cannot get things back into their place again. Everything looks “messy.” This is partly because, though you have torn neither muscle nor blood-vessel, you have torn something which binds skin and muscle and fat 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. =8.= 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 [Illustration: 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; _O_, small intestine; _P_, the cæcum, so largely developed in this and other herbivorous animals; _Q_, the large intestine. ] 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.