motions of this organ, as we use it in speaking, and eating, and swallowing.

16. The act of swallowing seems to you a very simple thing, but it is really a complicated act of a complicated set of machinery. There are many muscles that work together in doing it, and if they did not work right there would be failure in the motion, and choking would result. Observe that different muscles work in different parts of the act. When you first begin the act, the food is thrust back chiefly by the muscles of the tongue. As it goes back, the epiglottis, the lid of the larynx, is shut down by its muscles, so that the food may slide over it into the œsophagus that lies behind the windpipe. This lid, which thus shuts over the top of the passage to the lungs when we swallow, is raised up by its muscles when we speak or breathe. It is like a little tongue extending back from the root of the tongue itself. After the food has passed over this lid it goes down through the oesophagus into the stomach. But it does not simply fall down. The oesophagus is a tube, made in part of muscular fibres, so arranged that the food is really pushed by their action through this tube. So complicated is all this machinery, and so nice is its operation, that it would be impossible for any man to make a machine of the same shape that could perform the act of swallowing.

17. It seems to you a simple thing to speak. But every time that you speak there is a large number of muscles brought into action. There are the muscles.

What is said of the act of swallowing? Describe the different parts of this act.

of the chest that force the air out through the windpipe-the muscles that move the cords in the musicbox, the larynx-the muscles that move the epiglottis, the lid of the larynx-and the muscles that move the palate, the tongue, the jaws, and the lips. You cannot utter a word without the action of all these different muscles. And they must act just right, or there would be something wrong in the sound of the word.

18. As the different acts of speaking, laughing, breathing and swallowing follow each other so rapidly, there is vast variety in the changing action of the muscles. Especially busy are those little muscles that work the lid of the larynx, opening it when we breathe, or speak, or laugh, and shutting it down when we swallow. So securely do these door-keepers guard this door to the windpipe, that it is a rare accident for a crumb or a drop to get into it.

19. In performing the different motions that I have alluded to, such as swallowing, speaking, and the motions of the hand, there must be a concert or agreement of action among the muscles. The concert is as real as it would be if the muscles, like men that are pulling at ropes, understood each other, and agreed together as to what they would do. It is, indeed, a more perfect concert of action than ever occurs among a company of men in pulling ropes, especially when they pull upon different ropes. It is difficult

What different sets of muscles are engaged in the act of speaking? What is said of the variety of muscular action as we speak and breathe and laugh and swallow almost at the same time? What muscles are then especially busy? What is said of the concert of action in the muscles?

for each man to pull just enough and at exactly the right time. But there is no difficulty of this sort commonly with the muscles, however complicated the action may be. Thus in swallowing, each muscle acts just strongly enough and exactly at the right time.

20. I will now give you a general view of the muscles of the body. In Fig. 57 you have a side view of the muscles, that is, of all those that lie directly under the skin. There are many other muscles that lie under these that you see. You observe that the muscles are of various shapes and sizes, according to their situation and what they are intended to do. They are round, flat, long, short, fan-shaped, circular, &c. I will notice some of them particularly.

21. At a is a very large muscle at the top of the shoulder, that raises the arm, at the same time carrying it out from the body. At b is the muscle that bends the fore-arm at the elbow. At e is the muscle that acts in opposition to b and straightens the arm. The muscles at b and e are the same as those at 4 and 7 in Fig. 55. At d is a muscle that turns the forearm in such a way that the palm of the hand is upward, as seen in the figure. At g is a very large muscle. It comes from almost the whole length of the back-bone, and its tendon is fastened to the back part of the arm. Its office is to draw the arm back. Its tendon makes the rear boundary of the arm-pit. At i is one of the large, flat muscles of the abdomen. 7 and k are two muscles that move the thigh. At o

At

Describe the muscles of the body as represented in Fig. 57.

and p on the right thigh, and at n on the left, are seen three muscles that serve to throw the leg forward. They do this by pulling on the knee-pan. At q is the

tendon that forms the outer hamstring, and at r are the two tendons that form the inner one. The muscles that pull these hamstrings are on the back part of the thigh. When they act they make the leg swing backward, and therefore do just the opposite of what is done by the muscles n, o and p. At s is the muscle that makes the back of the calf of the leg. Its strong tendon, which is fastened to the bone of the heel, you can feel very plainly through the skin. It is this muscle, a part of which is represented in Fig. 54, at P.

22. The muscles díffer greatly in size. Some are very large, and some are exceedingly small. Contrast, for example, the muscles of the arm that wield the hammer and the axe, with the muscles that move the cords of the larynx in speaking and singing. These muscles of the voice are very delicate, and they produce the various notes by motions so small, that many of them could be measured by the breadth of a hair. Birds that mount up so beautifully in the air, have large muscles to work their wings. But the muscles that move their little musical cords, as they carol so sweetly, are so small, that it is difficult to find them when we dissect the larynx.

I will now notice some especial contrivances in the muscles and tendons.

23. There is a beautiful arrangement of the tendons in the toes and the fingers. In Fig. 58 is a representation of this arrangement in one of the fingers. a, b and c, are the three bones of the finger. At f

At

What is said of the size of the muscles? Give the contrasts mentioned.