12/27 The air-tubes and air-cells are well shown on the following page. The Voice-box.~--If you will place the ends of your fingers upon your throat just above the breast-bone, you will feel the windpipe, and may notice the ridges upon it. These are rings of cartilage, a hard substance commonly called gristle. The purpose of these rings is to keep the windpipe open. Close under the chin you can find something which feels like a lump, and which moves up and down when you swallow. |