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 confifting of two layers, or two 
mufcles decuffating and balancing each other, the motion of 
the ribs, upwards and downwards, is as direct, and with as 
_ little friion, as if it had been performed by ftraight or perpen- 
dicular mufcles. 
Vor. iit (aep ae XIV; 
