OF THE MUSCLES. 75 



I. We may observe, what I believe is universal, an ex- 

 act relation between the joint and the muscles which move 

 it. Whatever motion, the joint by its mechanical construc- 

 tion, is capable of performing, that motion, the annexed 

 muscles, by their position, are capable of producing. For 

 example ; if there be, as at the knee and elbow, a hinge 

 joint, capable of motion only in the same plane, the lead- 

 ers, as they are called, i. e. the muscular tendons, are 

 placed in directions parallel to the bone, so as, by the con- 

 traction or relaxation of the muscles to which they beloncr, 

 to produce that motion and no other. If these joints were 

 capable of a freer motion there are no muscles to produce 

 it. Whereas at the shoulder and the hip, where the ball 

 and socket joint allows by its construction of rotatory or 

 sweeping motion, tendons are placed in such a position, 

 and pull in such a direction, as to produce the motion of 

 which the joint admits. For instance, the sartorius or 

 tailor's muscle, arising from the spine, running diagonally 

 across the thigh, and taking hold of the inside of the main 

 bone of the leg a little below the knee, enables us, by its 

 contraction, to throw one leg and thigh over the other ; 

 giving effect, at the same time, to the ball and socket joint 

 at the hip, and the hinge joint at the knee. (PI. Ull. fig. 1.) 



There is, as we have seen, a specific mechanism in the 

 bones for the rotatory motions of the head and hands ; there 

 is also in the oblique direction of the muscles belonging to 

 them, a specific provision for the putting of this mechanism 

 of the bones into action. (PI. XII. fig. 2.) And mark the 

 consent of uses. The oblique muscles would have been 

 inefficient without the articulation ; the articulation would 

 have been lost, without the oblique muscles. It may be 

 proper however to observe with respect to the head, al- 

 though I think it does not vary the case, that its oblique 

 motions and inclination are often motions in a diagonal, 

 produced by the joint action of muscles lying in straight 

 directions. But, whether the pull be single or combined ; 

 the articulation is always such, as to be capable of obeying 

 the action of the muscles. The oblique muscles attached 



muscular faciculi, which are composed of fibres still smaller ; these 

 result from fibres of a less volume, until by successive division we ar- 

 rive at very small fibres no longer divisible. These muscular fibres 

 are longer or shorter according to the muscles to which they be- 

 long ; and every fibre is fixed by its two extremities to tendon or 

 aponeurosis, which are the " wires and strings" which conduct the 

 muscular power when they contract, Paxton, 



