2 6o OBSERVATIONS 



and that all the ribs in infpiration were moved upwards uni- 

 formly. 



The chief circumftances which prove beyond a doubt, that 

 the two rows of intercoftal mufcles confpire in elevating the 

 ribs, are, 



1. That 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. 

 rig. 9. 



2. That 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 vertebrae, 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, connected with the vertebras 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- 

 je6t, from the vertebrae 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 



diitances 



