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CLX VII. Of the fiower of the muscles; of the mode of estimating thatjiower. 

 The actual power of the muscles is immensely great, seems to grow in 

 proportion to the resistance which it meets with, and can never be esti- 

 mated with precision. Borelli was guilty of a serious mistake, in esti- 

 mating the force of a muscle by its weight, compared to that of another 

 muscle, for muscles may contain cellular tissue, fat, tendinous parts, and 

 aponeuroses, without being the more powerful. Their strength is al- 

 ways proportioned to the number of their fleshy fibres; hence, Nature has 

 multiplied those fibres in the muscles which are intended for powerful 

 action. And in order that this great number of muscular fibres might 

 not add too much to the bulk of the limbs, they are made shorter, by 

 bringing near to each other their insertions, which occupy extensive sur- 

 faces, whether aponeurotic or osseous. We may, in general, judge of the 

 power of a muscle, by the extent of the surfaces to which its fleshy fibres 

 are attached ; thus, the gamelli and the soleus have short compressed 

 fibres, and lie obliquely between two large aponeuroses. 



If the force with which a muscle contracts, is proportioned to the 

 number of its fibres, the degree of decurtation of which it is capable, and 

 consequently, the range of motions which it can communicate to the 

 limbs, are proportioned to the length of the same fibres*. Thus, the sar- 

 torius, whose fibres are longer than any in the human body, is also capa- 

 ble of most contraction, and performs the most considerable motions of 

 the leg. It is impossible to fix any precise limits to the decurtation of 

 every particular muscular fibre ; for, if the greater part of the long mus- 

 cles of limbs lose little more than a third of their length, in contracting, 

 the circular fibres of the stomach, which, in its greatest dilatation, form 

 circles nearly a foot in diameter, may contract, to such a degree, when 

 this organ has been long empty, as to form rings of scarcely an inch in 

 circumference. In cases of extreme elongation or constriction, does the 

 change that take place, affect the molecules that form the muscular fibre, 

 or the substances which connect them together, or does it affect, at once, 

 both the fibre and the parts by which these fibres are united together? 



However great the power of the muscles may be, a great part of this 

 power is lost, from the unfavourable disposition of ourorgans of motion; 

 the muscular powers, almost always parallel to the bones which they are 

 to move, act with the more disadvantage on these levers, as the main 

 line of their direction is further from the perpendicular, and is nearly 

 parallel to them. 



The greater part of the muscles are, besides, inserted in the bones, 

 very near the articulations or the centre of motion, and move them as 

 levers of the third kind, that is, are always placed between the fulcrum 

 and the resistance; by multiplying thus, in the animal machine, the levers 

 of the third kind, Nature has lost in power, but has gained in strength, 

 for, in this kind of lever, the power moves through a very small space, but 

 makes the resistance most through a very considerable one. Besides, the 

 fleshy fibres, in shortening themselves, do not act directly on the tendon 

 in which the muscle terminates, these fibres generally join, in an ob- 



* Besides these data, \ve should take into consideration the energy of the nervous 

 impulse, under which voluntary muscles contract. We perceive nearly as great differ- 

 ences, in the activity, the intensity, the frequency, and the continuance of muscular 

 contraction, result from the state of the nervous system, even in health, as may be im- 

 puted to the form and size of the muscles themselves, unless the difference of their con- 

 stitution or size, be very considerable. Copland. 



