On the MUSCLES. 261 



diftances between their heads and the fternum. The continued 

 perpendicular line reprefents the diflance of the middle of each 

 rib from a ftraight line drawn between its two ends. The 

 numbers 1, 2, 3, 4, 5, 6, 7, exprefs firft, fecond, &c. ribs, of 

 which the firft is the fhorteft and innermoft, and the feventh the 

 longeft and outermoft. The other numbers annexed denote 

 eighths of an inch. 



4. To determine the effect of the contraction of any mufcle, 

 I apprehend, we need only to obferve in the dead body what 

 the fituation is in which the mufcle in queftion is relaxed. Ap- 

 plying this rule, we fliall find, that the whole intercoftal 

 mufcles, internal as well as external, are (hortened when we 

 elevate the ribs and place them in that fituation in which we 

 find they are in infpiration. 



5. If the internal intercoftal mufcles had been intended for 

 the depreflion of the ribs, we certainly (hould not have found 

 them continued to the fternum, becaufe their anterior ends are 

 fixed above to the edge of the fternum, or fo near to the infer- 

 tion of the cartilage of the upper rib in the fternum, and 

 their inferior ends are, in confequence of their obliquity, fixed 

 to the under rib fo much farther from the fternum, that they 

 muft adt upon the under rib with more advantage of lever, or 

 are intended for its elevation. 



On the other hand, if the internal intercoftals had been in- 

 tended for the depreflion of the ribs, we certainly lhould have 

 found them continued backwards to the fpine, becaufe, from 

 their obliquity, their under end would have been fixed to the 

 vertebrae or nearer to the head of the rib, and their upper end 

 at fuch a' diftance from it, that this portion of the mufcle 

 would have been better calculated than any other portion of it 

 for the depreflion of the rib. 



6. In a few experiments which I made on living animals, 

 foon after I began to ftudy anatomy, and which I repeated af- 

 terwards, particularly in 1770, 1 faw plainly, as DrHALLER had 



done ? 



