158 THE RIBS. 



turning round. But then it is likewise as evident, that even 

 the motion upwards and downwards can be but small in any 

 one rib at the articulation itself. But as the ribs advance 

 forwards, the distance from their centre of motion increasing, 

 the motion must be larger ; and it would be very conspicuous 

 at their anterior ends, were they not resisted there by the car- 

 tilages which yield so little, that the principal motion is per- 

 formed by the middle part of the ribs, which turns outwards 

 and upwards, and occasions the twist remarkable in the long 

 ribs at the place near their fore end where they are more 

 resisted. 



The ribs differ from each other in the following respects : 

 The upper rib is the most crooked ; and as they descend 

 they become straighter. Their obliquity, with respect to the 

 spine, increases as they descend, so that though their distances 

 from each other are nearly equal at their back part, yet at their 

 fore ends the distances between the lower ribs must increase. 

 In consequence of this increased obliquity of the lower ribs, 

 each of their cartilages makes a greater curve in its progress 

 from the rib towards the sternum ; and the tubercles that are 

 articulated to the transverse processes of the vertebrae, have 

 their smooth surfaces gradually facing more upwards. The 

 ribs becoming thus more oblique, while the sternum advances 

 forwards in its descent, makes the distance between the sternum 

 and the anterior end of the lower ribs greater than between the 

 sternum and the ribs above ; consequently, the cartilages 

 of those ribs that are joined to the breast bone are longer in the 

 lower than in the higher ones. These cartilages are placed 

 nearer to each other as the ribs descend, which occasions their 

 curvature to be greater. 



The length of their ribs increases fromthe first and upper- 

 most rib, as far down as the seventh ; and from that to the 

 twelfth, it gradually diminishes. The superior of the two 

 surfaces, by which the ribs are articulated to the bodies of the 

 vertebras, gradually increases from the first to the fourth rib, 

 and is diminished after that in each lower rib. The distance 

 of their angles from the heads always increases as they 



