ANIMAL AND VEGETABLE 178 



are called the muscle-tendons. They are sometimes short, 

 sometimes long, thicker or thinner according to the size of 

 the muscle, and they serve to attach the muscles firmly to 

 the bones, to which, acting like ropes, they transmit the 

 tension of the muscles. One of the two bones to which a 

 muscle is attached is usually less mobile than the other, 

 so that when the muscle shortens, the latter is drawn down 

 against the former. In such a case the point of attachment 

 of the muscle to the less mobile bone is called its origin, 

 while the point to which it is fixed on the more mobile bone 

 is called its attachment (epiphysis). For instance, there 

 is a muscle which, originating from the shoulder-blade and 

 collar-bone, is attached to the upper arm-bone ; when this 

 muscle is shortened the arm is raised from its perpendicular 

 pendant position into a horizontal position. A muscle is 

 not always extended between two contiguous bones. 

 Occasionally passing over one bone, it attaches itself to the 

 next. This is the case with several muscles which, origin- 

 ating from the pelvic bone, pass across the upper thigh-bone 

 and attach themselves to the lower thign-bone. In such 

 cases the muscle is capable of two different movements : 

 it can either stretch the knee, previously bent, so that the 

 upper and the lower febigk-bones are in a straight line, or 

 it can raise the whole extended leg yet higher and bring it 

 nearer to the pelvis. But the points of origin and of 

 attachment of muscles may exchange offices. When both 

 legs stand firmly on the ground the above-mentioned 

 muscles are unable to raise the thigh ; instead, on shorten- 

 ing, they draw down the pelvis, which now presents the 

 more mobile point, and thus bend forward the whole 

 upper part of the body. ... In a previous examination 

 of the action of muscle we have dealt with an imaginary 

 muscle, the fibres of which were of equal length and par- 

 allel to each other. Such muscles do really exist, but they 

 are rare. When such a muscle shortens, each of its fibres 



