INSPIRATION 255 



'nward is counteracted by the outward pressure of the' abdominal viscera, 

 and by the action of the quadrati himborum, which by their attachment to 

 the last ribs fix these and, in case of deep inspiration, may even pull them 

 downward. The serrati postici inferiores also aid, being attached to the 

 four lower ribs. 



Changes in the lateral and antero-posterior diameters are effected by the 

 raising of the ribs, which are attached very obliquely to the spine and sternum. 

 The elevation of the ribs takes place both in front and at the sides the 

 hinder ends being prevented from performing any upward movement by 

 their pivot attachment to the spine. The movement of the front extremities 

 of the ribs is of necessity limited by an upward and forward movement of the 



PIG. 230. Diagram of Axes of Movement of Ribs. 



sternum to which they are attached, the movement being greater at the lower 

 end than at the upper end of the sternum. 



The axes of rotation in these movements are two: one corresponding 

 with a line drawn through the two articulations which the rib forms with 

 the spine, a, b, figure 230, and the other with a line drawn from one of these 

 (head of rib) to the sternum, A B, figure 230; the motion of the rib around 

 the latter axis being somewhat after the fashion of raising the handle of a 

 bucket. The elevation of the ribs is accompanied by a slight opening out of 

 the angle which the bony part forms with its cartilage, and thus an additional 

 means is provided for increasing the antero-posterior diameter of the chest. 

 The movements of all the ribs except the twelfth consist of a rotation up- 

 ward, forward, and outward. The twelfth presents only rotation down- 

 ward and backward. 



