THE BODY.] 



PHYSIOLOGY, 



19 



spinal cord or the brain. If you try to trace the 

 same nerves in the other direction, you will find them 

 branching into smaller and smaller nerves, until they 

 become too small to be seen. If you take a micro- 

 scope you will find they get still smaller and smallei 

 until they become the very finest possible threads. 



The blood-vessels in a similar way join together 

 into larger and larger tubes, which last all end, as we. 

 shall see, in the heart. Every part of the body, 

 with some few exceptions, is crowded with 

 nerves and blood-vessels. The nerves all 

 come from the brain or spinal cord — the 

 vessels from the heart. So that every part 

 of the body is governed by two centres, the 

 heart, and the brain ^- -rp'^^^l cord. You will 

 see how important ic is to remember Jiis when we 

 get on a little further in our studies. 



12. Well, then, the body is made up in this way. First 

 there is the head. In this is the skull covered with 

 skin and flesh, and containing the brain. The skull 

 rests on the top of the backbone, where the head 

 joins the neck. In the upper par; of the neck, the 

 throat divides into two pipes or tubes — one the wind- 

 pipe, the other the gullet. These running down the 

 neck m front of the vertebral column, covered up 

 by many muscles, when they get about as far down as 

 the level of the shoulders, pass into the great cavity 

 of the body, and first into the upper part of it, or 

 chest. 



Here the windpipe ends in the lungs, but the gullet 

 runs straight through the chest, lying close at the 

 back on the backbone, and passes through a hole in 

 the diaphragm into the abdomen, where it swells out 



c 2 



