On the MUSCLES. 261 
diftances between their heads and the fternum. The continued 
perpendicular line reprefents the diftance 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 mutfcle, 
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 fhall find, that the whole intercoftal 
mufcles, internal as well as external, are f{hortened when we 
elevate the ribs and place them in that fituation in which we 
find they are in infpiration. 
5. Ir the internal intercoftal mufcles had been intended for 
the depreflion of the ribs, we certainly fhould 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 
mutt act upon the under rib with more advantage of lever, or 
are intended for its elevation. 
On the other hand, if the internal eet had been in- 
tended for the depreffion of the ribs, we certainly fhould have 
found them continued backwards to the fpine, becaufe, from 
their obliquity, their under end would have been fixed.to the 
vertebrz 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 depreffion 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 Dr HanueR had 
done, 
