RESPIRATION. 201 



ribs are raised, their vertebral extremity rotates, remaining in its 

 place ; the rest of the rib rises, each part of course the more, the 

 more distant it is from the vertebra, and the lower margin is drawn 

 rather outwards; and with the ribs the sternum rises. The 

 chest thus becomes both broader and deeper from front to back. r 

 " Between the edges of the ribs lie two strata of intercostal 

 muscles, differing in the direction of their fibres, but conspiring " 

 to elevate the ribs or depress them, just as the higher or 

 lower rib happens to be the more fixed. The one is external, 

 placed between the vertebrae and the cartilages, and its fibres 

 run forwards and downwards : the other internal, placed be- 

 tween the sternum and the angle or curve of the rib near the 

 spine, and its fibres run downwards and backwards. Ordi- 

 narily, they act as muscles of inspiration, and raise the ribs, 

 because the lower rib is more movable than the one above it. 



Between the higher and 

 middle rib, except near the 

 sternum, is seen the internal 

 intercostal : between the 

 lower and middle, the ex- 

 ternal. 



r Although each lower rib among the first eight must execute a greater extent 

 of motion, from being longer than the one above, yet the first is asserted by Dn 

 Magendie to be absolutely more movable than the second, the second than the 

 third, &c. ; and this because the first has but one articular surface, is articulated 

 with but one vertebra, and possesses neither internal nor costo-transverse ligament, 

 and has the posterior ligament horizontal, and because slight shades of difference 

 exist in the disposition of the ligaments of the six other ribs. Precis Elemen- 

 taire, t. ii. p. 317. 



