On the MUSCLES. 265 



Upon the whole, by the obliquity of the intercoftal muf- 

 cles, the motion of the ribs is very much greater than could 

 have been performed by ftraight mufcles placed between them : 

 At the fame time, by their confifling of two layers, or two 

 mufcles decuflating and balancing each other, the motion of 

 the ribs, upwards and downwards, is as direct, and with as 

 little friction, as if it had been performed by ftraight or perpen- 

 dicular mufcles. 



Vol. III. L 1 XIV, 



