The Minoan and Mycenaean element in Hellenic life / [Sir Arthur Evans].
- Evans, Arthur, Sir, 1851-1941.
- Date:
- 1914
Licence: In copyright
Credit: The Minoan and Mycenaean element in Hellenic life / [Sir Arthur Evans]. Source: Wellcome Collection.
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![6R0UP 4—PHYS10L06Y & HEALTH ' THE BODY & ITS MAINTENANCE—CHAPTER 15 The Three Orders of Levers in the Body. How the Erect Position is Maintained. Waiking, Running, and Jumping. MOTION AND LOCOMOTION Motion in itself is no more a proof of life in a man than in a steam-engine ; it is the method by which it is produced in man that differentiates him from a machine. IMotion and locomotion are not the same. Motion is move- ment only, but locomotion is movement from one place to another ; in walking we get both. A great deal of motion takes place in the body apart from locomotion, although, in fact, the body as a whole does not change its place. For motion or locomotion four structures at least are necessary as regards the mechanism. Something to be moved—the bones ; a place where they move—the joints ; machinery that moves them—the muscles; and a force that controls the machinery—the nerves ; and all movements involving these structures take place according to mechanical laws. These, then, we will briefly consider. A System of Levers. The principle with which we are most concerned is that of leverage, or movement by means of levers. A lever is simply a bar that hfts (French lever— to lift), which may be either straight or crooked, and made of any rigid substance, such as wood, iron, or bone. All our bones are used as levers or bars. [See page 1025.] Now, as a rule, we can do so much more work with levers than we can do without them that Archimedes, who discovered their use, said that if he had a lever long enough, and a fulcrum to rest it on, he could move the world. The parts in a lever are three in number. They are the Julcrum (F), or the fixed point on which the lever moves, which in the body is invariably a joint; the power (P), or the force that moves the lever ; and the weight (W), or the object that is moved. Orders of Levers. The orders of levers vary according to their relative position, thus : WFP is the first order—that is, when the fulcrum is in the middle. PWF is the second order—that is, when the weight is in the middle. WPF is the third order—that is, when the power is in the middle. Levers of the Body, Now, all three orders of levers are used in the body [71], although the third is undoubtedly the favourite, for a reason that will be evident. Tapping the foot on the ground, raising the head off the chest, and straightening the arm are examples of the first order. Thus: F. P. foot ankle-joint muscles of calf head joint with spine muscles of spine hand elbow-joint triceps muscle Standing on tiptoe is an instance of the second order. P. W. F. calf-muscle body toes resting on ground and act- ing as a joint. Bending the arm, closing the jaw, are examples of the third order, thus : W. P. F. hand biceps elbow-joint jaw jaw muscles jaw joint Respecting this third order, observe thav the power, or the muscle, is attached between the fulcrum in the joint at one end and the weight to be lifted at the other. The nearer the muscle is attached to the weight to be lifted the more it has to be contracted to lift the weight, whereas the nearer it is attached to the fulcrum the less it has to contract, but greater force is needed. For instance, consider the attachment of the muscles of the arm anri leg. You will have noticed how all the body levers have the fulcrum close to the power at tljo end of the bar. Thus, the elbow-joint is cloil' to the point of the elbow behind, and the ankle i close to the heel; and you will also have noticA. in the same way that in every case the muscle^ are attached as near to the fulcrum, or joint, ds possible. Those that lift the arm are fixed just below the shoulder ; those that lift the forearn are fixed just in front of the elbow ; those tha move the thigh just below the hip ; and those that move the leg just below the knee. Why a Muscle is Attached near the Fulcrum. The object is to give the greatest movement of the limb with the least contrac- tion of the muscles. If you take two bits of firewood a foot long, and join them together at one end with a tack, open them at right angles, and tie a string from one end to the other, it will be 17 in. long. To bring the ends of the tAvo pieces together by pulling on the string, you must use up all the 17 in. ; but if you tie one end of the string close in front of the joint in the way our muscles are fixed, you will find that, though you have to pull harder to bring the pieces of wood together, you only use up about 1 in. in length of the string to move the ends of the firewood 17 in. [72]. By this contrivance, therefore, the slighi contraction of the muscles can move the lim’. a great distance. When you kick a football, yo- foot goes through a great space, but the mu' that moves it only contracts an inch or two. Shoulder and Hip Contrasted. So special joints in the body call for a brief co . sideration. Let us first contrast the shouldc. and the hip. The shoulder is not a fixed joint,, but can be moved backwards and forwards t< ■ a certain extent. It is supported behind by, THIS GROUP EMBRACES ANATOMY, PHYSIOLOGY, AND HYGIENE 1G19](https://iiif.wellcomecollection.org/image/b24878959_0057.jp2/full/800%2C/0/default.jpg)
