528 PHILOSOPHICAL TRANSACTIONS. [aNNO 1795. 



plicity of form, in the muscular structure of this species of hydatid, makes it 

 evident that the complex organization of other muscles is not essential to their 

 contraction and relaxation, but superadded for other purposes ; v;hich naturally 

 leads us to suppose that this power of action, in living animal matter, is more 

 simple, and more extensively diffused through the different parts of the body, 

 than has been in general imagined. 



From these observations we shall find, that the inquiries hitherto made into 

 the principle of muscular motion, by investigating the muscles of the more per- 

 fect animals, which are most remarkable in their effects, and obviously most de- 

 serving of attention, have been too confined. From our inquiry into the struc- 

 ture of muscles, in different animals, we readily discover that those above-men- 

 tioned, though the most perfect in their organization, are at the same time so 

 complicated, for the purpose of adapting them to a variety of secondary uses, 

 that they become, of all others, the kind of muscle least fitted for the investiga- 

 tion of the principle itself. In the present imperfect state of our knowledge re- 

 specting animal life and motion, a physiologist, who would select a complex 

 muscle, with the view of discovering, from an examination of its structure, the 

 cause of muscular contraction, would resemble a man, ignorant of mechanics, 

 who should consider a watch as the machine best adapted to assist his inquiries 

 respecting the elastic principle of a spring ; which at first sight must appear ab- 

 surd. For though the spring is the power by which the motions are all produced, 

 the machine is so complicated with other important or necessary parts, that the 

 spring itself is not within the reach of accurate observation. 



To prosecute an inquiry into the cavise of muscular motion, with the greatest 

 probability of success, recourse should be had to muscles which are in themselves 

 the most simple ; and we should endeavour to ascertain what organization, or 

 mechanism, is essential to this action in living animal matter ; by which means 

 we should acquire a previous step to the investigation of the principle itself. The 

 complex muscles in the more perfect animals, from their structure and applica- 

 tion, open a wide field of inquiry ; ^pr we shall find that it is from their differ- 

 ent organizations that they are enabled to perform the various actions of the 

 body ; actions too powerful and extensive for muscles to effect, unaided by such 

 complication of structure, and the advantages derived from it. 



In the present lecture, I shall confine myself to the consideration of the most 

 important uses of the complex structure of muscles, and by this means make it 

 evident, that they are not indebted to it for the principle on which muscular mo- 

 tion depends. These complications are necessary to supply the muscle with 

 nourishment, for the continuance of its action ; to give it strength ; to enable 

 it to vary its contraction from the standard or ordinary quantity ; and to 



