OF THE MUSCLES' < 85 



sent. This last is a faculty, which, upon some extraordi- 

 nary occasions, he may desire to possess ; but the other is 

 what he wants and uses every hour and minute. -In like 

 manner, a husbandman or a gardener will do more execu- 

 tion, by being able to carry his scythe, his rake or his flail, 

 with a sufficient despatch through a sufficient space, than 

 if, with greater strength, his motions were proportionably 

 more confined and slow. It is the same with a mechanic in 

 the use of his tools. It is the same also with other animals 

 in the use of their limbs. In general, the vivacity of their 

 motions would be ill exchanged for greater force under a 

 clumsier structure. 



We have offered our observations upon the structure of 

 muscles in general ; we have also noticed certain species 

 of muscles ; but there are also single muscles, which bear 

 marks of mechanical contrivance, appropriate as well as 

 particular. Out of many instances of this kind we select 

 the following : — 



I. Of muscular actions, even of those which are well 

 understood, some of the most curious are incapable of pop- 

 ular explanation ; at least without the aid of plates and 

 figures.* This is in a great measure the case, with a very 

 familiar, but, at the same time, a very complicated motion, 

 that of the lower jaw; and with the muscular structure by 

 which it is produced. One of the muscles concerned, may, 

 however, be described in such a manner, as to be, X thinks 

 sufficiently comprehended for our present purpose. The 

 problem is to pull the lower jaw down. The obvious method 

 should seem to be, to place a straight muscle, viz. to fix a 

 string from the chin to the breast, the contraction of which 

 would open the mouth, and produce the motion rec^uired at 

 once. But it is evident that the form and liberty of the 

 neck forbid a muscle being laid in such a position ; and 

 that, consistently with the preservation of this form, the 

 motion which we want, must be effectuated, by some muscu- 

 lar mechanism disposed further back in the jaw. The me- 

 chanism adopted is as follows: (PI. XV. fig. 1, 2.) A 

 certain muscle called the digastric rises on the side of the 

 face, considerably above the insertion of the lower jaw ; 

 and comes down, being converted in its progress into a 

 a round tendon. Now it is evident, that the tendon, whilst 

 it pursues a direction descending towards the jaw, must> 

 by its contraction, pull the jaw up, instead of down. What 



* The want of the aid of plates and figui'es, which the author here 

 expresses, is now suppUed in this Boston edition, 



