in] of the New Physics. 69 



recognized that nerves were concerned in the action, it being 

 generally supposed that animal spirits passing along the nerves 

 to the muscle, provoked in some way or other the movement. 

 In the muscle itself two parts were recognized : the fibres of 

 the muscle which, though possessing a nature of their own, 

 passed into and were continuous with the fibres of the tendon 

 at each end, and the flesh, 'caro,' which filled up the interstices 

 between the fibres and adapted itself to them, but which 

 otherwise was comparable with the flesh, ' caro,' or parenchyma 

 of other organs, such for instance as the liver. According at least 

 to general opinion, the contraction, that is the shortening and 

 hardening of the muscle as a whole, was carried out not by the 

 flesh, 'caro,' but by the fibres of the muscle, the power of the 

 fibres to effect this being due to the animal spirits reaching 

 them along the nerves. 



Vesalius, passing lightly over this, as over other problems 

 distinctly physiological rather than anatomical, and this as we 

 have seen was his wont, has little to say about it, but that 

 little goes straight to the root of the matter. He saw clearly 

 that the contractile power of the muscle resides in the actual 

 muscular substance, not in the fibres of the ligament or tendon 

 which spread out into the muscle's belly, nor in the nerves 

 distributed in it, though these played their part as carriers of 

 the animal spirits. This is what he says : 



" Muscle therefore, which is the instrument of voluntary 

 " movement as the eye is the instrument of vision and the 

 Ci tongue of taste, is composed of the substance of the ligament 

 " or tendon divided into a great number of fibres and of flesh 

 " containing and embracing these fibres. It also receives 

 " branches of arteries, veins and nerves, and by reason of 

 " the presence of the nerves is never destitute of animal 

 "spirits so long as the animal is sound and well. Now I 

 "do not regard this flesh as merely a foundation or basis, 

 "as it were a bed or support by which the fibres and the 

 "above-mentioned divisions of the nerves are held together. 

 "Nor do I with Plato and Aristotle (who did not at all 

 "understand the nature of muscle) attribute to the flesh so 

 " slight a duty as to serve, after the fashion of fat or grease 



