On the MUSCLES. 26$ 



But to fhew the fallacy of this, I need only to add to what 

 has been before obferved, that we can perform a full infpiration, 

 without bringing the upper rib, or top of the fternum, up- 

 wards or nearer to our head ; whereas the pretended demon- 

 ftration refts entirely on the fuppofition, that all the ribs, not 

 excepting the firil and fternum, have a large play upwards and 

 downwards alternately. Stop the play of the firft rib, or fup- 

 pofe it to be fixed in its place, which is the fa 61, and the boaft- 

 ed demonftration is annihilated. 



The late opinion of Sabatier *, that both rows of inter- 

 coftal mufcles ferve for expiration, and that the ribs are elevated 

 by the fcaleni and ferrati poftici fuperiores, which are fixed to a 

 few only of the upper ribs, fcarcely merits a comment. It is 

 refuted by what is above mentioned, and by the want of the 

 external intercoftals near to the fternum, and of the internal 

 near to the fpine ; for intercoftals at thofe places would have 

 ferved to deprefs the ribs more powerfully than in any other 

 part of the thorax. 



Let us now confider the purpofe, 



First, Of the obliquity of the fibres in the intercoftal 

 mufcles, and, 



Secondly, Of their, being difpofed in two layers, the fibres 

 of which decuflate each other. 



It is evident, that the obliquity of the fibres here is not in- 

 tended to increafe their number, or the ftrength of the mufcle, 

 becaufe the fibres would have been more numerous if they had 

 patted directly from the one rib to the other, or had been in- 

 ferted into the ribs at right angles. 



I apprehend, therefore, that we are to explain the reafons 

 of the ftruclure in the following manner : 



Nature, in order to give protection to the heart and lungs, 

 has formed the ribs as broad and fiat as poflible, or left no 

 more fpace between them than is required for lodging mufcles 



for 



* See Anatom. T. 3. p. 465. 7. m.. 



