Physiology of the Muscles. 499 



connected with a fibre of tendon tissue. The tendons connect the mus- 

 cle with the bones, or other part to be moved. The attachments of the 

 muscles to the parts to be moved, are generally such that power is sac- 

 rificed to speed of movement. Thus the biceps muscle of the arm, 

 which is attached at its upper end, by two prongs, to the shoulder blade, 

 and runs down the humerus, is connected with the radius bone of the 

 fore-arm only about an inch and a half from the. joint. (See fig. 86.) 

 So that a contraction of the muscle amounting to an inch, will move the 

 hand about ten times as far, with a loss of nine-tenths of the power. 

 The biceps of the thigh is arranged in an analogous manner. 



There are arrangements in some cases which add to the power of mus- 

 cles. Thus the patella, or knee pan, is a projecting bone to which the 

 extensor muscles are attached and which add to their power by adding 

 to their leverage in the straightening of the leg. In the case of the 

 superior oblique muscle of the eye, the muscle is carried through a car- 

 tilaginous pully which is attached to the frontal bone, and is doubled 

 back on itself, so that when it contracts, its point of insertion on the 

 globe of the eye is moved in a direction contrary to the direction of the 

 contraction. The muscles in their natural attachments are in a state of 

 tension so that if one were cut in two it would shrink in length. Muscles 

 on opposite sides of a limb, as the flexors on the inside of the leg and 

 the extensors on the outside, have a tendency to draw the bones to- 

 gether in their sockets. When one of these is contracted its opposite is 

 stretched. 



A muscle being a generator of electricity, it may be made a part of a 

 circuit, and when out of the. circuit shows the positive and negative ten- 

 sions which are to be observed in the metallic battery. A muscle prism 

 is a bundle of straight parallel fibres cut off square at both ends. The 



FIG. 233.^! bundle of muscle fibres 

 forming a regular Muscle Prism. 



gj*pj . j^jiti/'i ^^ 



FlG. 233. 



surface of this which exposes the sides of the fibres is called the longi- 

 tudinal section of the prism, while that which shows their ends is the 

 cross-section. An imaginary line passing around the prism across the 

 fibres and dividing the prism into two symmetrical halves is called the 

 equator, because at every point on such a line a higher positive tension 

 prevails than is to be found on either side of it. 



Ever3 T point on the equator has a greater positive tension than any 

 other point on the longitudinal section or the cross-section. The posi- 

 tive tension decreases along the longitudinal section each way from the 

 equator, until at the point where the longitudinal meets the cross-section, 



