170. Persons with small muscles, and largely developed nervous systems, will sometimes exhibit very great muscular power for a time; but it will not be of long continuance, unless the brain is functionally diseased, as in hysteria, delirium of fever, insanity, &c. Men of large muscles and small nerves can never perform feats of great strength; but they have the power of endurance, and are better capacitated for continued labor. Thus we cannot judge of the ability of persons to make exertions and continue them, by their stature alone. Strength, and the power of endurance, are the result of a combination of well-developed muscles, large nerves, and a full-sized, healthy, and active brain. _Observation._ The muscles of fishes are large, and the nerves distributed to them, comparatively small. The muscles of birds are small, but their fibres are very compact. The nerves appropriated to the muscles that are called into action in flying, are large as well as numerous. 171. The contractile portion of a muscle is, in general, at a distance from the part to be moved. Thus the principal muscles that move the fingers are situated upon the forearm; and when the limb is nearly or quite extended, the angle formed by the part to be moved and the contractile muscles is small. Again, the attachment of the muscles to the part to be moved is near the joint that forms the fulcrum, (fig. 45.) By these arrangements there is a loss of power; but we are compensated for this disadvantage by increased celerity of movement, beauty of form, and adaptation of the limbs to the varied pursuits of man. -=-=-=-=-=-=-=-=-=-=-=-= 170. What is said of those persons who have small muscles and largely developed nervous systems? Of those who have large muscles and small nerves? Upon what do strength and the power of endurance depend? 171. Why is there a loss of power in the action of the muscles? -=-=-=-=-=-=-=-=-=-=-=-= _Illustration._ The muscle that bends the elbow acts at disadvantage, and this is greatest when the arm is nearly or quite extended, as the angle of action is then least. This disadvantage is further increased by the attachment of the motive muscles near the joint. 172. The number of muscles which are called into action in the movements of the different joints, varies. The hinge-joints, as the elbow, have two sets of muscles--one to bend the joint, the other to extend it. The ball and socket joints, as the shoulder, are not limited to mere flexion and extension. No joint in the system has the range of movement that is possessed by that of the shoulder. By the action of the muscles attached to the arm, it is not only carried upward and forward, but forward and backward. Hence the arm may be moved at any angle, by a combined action of its muscles.