260 OBSERVATIONS 
and that all the ribs- in infpiration were moved upwards uni- 
formly. A; 
Tue chief circumftances which prove beyond a doubt, that 
the two rows of intercoftal mufcles confpire in elevating the 
ribs, are, 
1. TuaT the firft rib is fo much fixed at both its ends as 
to ‘be almoft immoveable, and its cartilage, inftead of being 
connected to the fternum by a capfular ligament, or articulated 
with it in the fame manner as the cartilages of the other ribs, 
grows as firmly to the fternum as to the rib. See T. 3. 
fig. 9. 
2. TuatT the fecond rib is more fixed than the third, and 
the third more fixed than the fourth, and fo on downwards. 
3. THaT as the ribs, from the firft rib downwards, grow 
gradually longer, and defcribe portions of larger circles, we may 
obferve, that in general, or when we examine a middle portion of 
the intercoftal mufcles, or a portion half-way between the fternum 
and vertebrz, the infertion of the lower end of the portion is 
at a greater diftance from either end of the lower rib, or from 
a ftraight line drawn between the two ends of that rib, than its 
origin in the rib above is from the two ends of that rib, or from 
a ftraight line drawn between them. Hence, whether we con- 
fider the head of the rib, conne&ted with the vertebre as its 
centre of motion, or whether we confider the rib as moving 
upon a ftraight line or axis drawn between its two ends, it fol- 
lows, that a mufcle placed between two ribs acts with a longer 
lever upon the under rib than upon the upper one, and there- 
fore muft elevate the under rib. That the force of this argu- 
ment might be more readily underftood, I have laid leaden 
probes along each of the feven uppermoft ribs of an adult fub- 
ject, from the vertebrz to the fternum, and have reprefented 
their lengths and curvatures in T. IV. The crooked continued 
lines reprefent the lengths and curvatures of the different ribs 
and their cartilages. The ftraight dotted lines reprefent the 
diltances. 
