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ARTICULATION OF THE MANUBRIUM AND BODY OF STERNUM 305 



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attachments of their anterior extremities, and it is convenient therefore to consider separately 

 the movements of the ribs of the three groups vertebrosternal, vertebrochondral, and vertebral. 



Vertebrosiernal Ribs (Figs. 316, 

 3 17). The first rib differs from the 

 others of this group in that its at- 

 tachment to the sternum is a rigid 

 one; this is counterbalanced to some 

 extent by the fact that its head 

 possesses no interarticular ligament, 

 and is therefore more movable. The 

 first pair of ribs with the manu- 

 brium sterni move as a single piece, 

 the anterior portion being elevated 

 by rotatory movements at the 

 vertebral extremities. In normal 

 quiet respiration the movement of 

 this arc is practically nil; when it 

 does occur the anterior part is 

 raised and carried forward, increas- 

 ing the antero-posterior and trans- 

 verse diameters of this region of the 

 chest . The movement of the second 

 rib is also slight in normal respira- 

 tion, as its anterior extremity is 

 fixed to the manubrium, and pre- 

 vented therefore from moving up- 



FIG. 316. Lateral view of first and seventh ribs in position, show- 

 ing the movements of the sternum and ribs in A, ordinary expiration; 

 B, quiet inspiration; C, deep inspiration. 



ward. The sternocostal articulation, 

 however, allows the middle of the 

 body of the rib to be drawn up, and 



in this way the transverse thoracic diameter is increased. Elevation of the third, fourth, fifth) 

 and sixth ribs raises and thrusts forward their anterior extremities, the greater part of the move- 

 ment being effected by the rotation of the rib neck backward. The thrust of the anterior 

 extremities carries forward and upward the body of the sternum, which moves on the joint 



FIG. 317 . Diagram showing the axes of movement 

 (A B and C D) of a vertebrosternal rib. The inter- 

 rupted lines indicate the position of the rib in 

 inspiration. 



FIG. 318. Diagram showing the axis of movement 

 (A B) of a vertebrochondral rib. The interrupted lines 

 indicate the position of the rib in inspiration. 



between it and the manubrium, and thus the antero-posterior thoracic diameter is increased. 

 This movement is, however, soon arrested, and the elevating force is then expended in raising 

 the middle part of the body of the rib and everting its lower border; at the same time the 

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