THE MECHANICS OF RESPIRATION 317 



above and with the body of the sternum below. The freedom of move- 

 ment at the angle which the mamibrium makes with the sternum at this 

 joint is related to the type of breathing. When the lower portion of the 

 sternum is elevated during inspiration, the movement of the joint is not 

 free, but when the sternum is retracted, the movement at the angle may 

 amount to 16. Lack of movement of the sternal manubrial joint has 

 been considered by some physicians as one of the predisposing causes of 

 pulmonary tuberculosis. During inspiration, the first rib and its anterior 

 attachments are raised by the scaleni, and serve as a point towards which 

 the second, third, fourth and fifth ribs are elevated. During expiration, 

 they are depressed toward the lower ribs, which form a more or less 

 fixed base. 



The combined effect of these influences is to produce a motion of the 

 upper ribs which is described by the clinician as being undulatory. This 

 movement is more apparent in the upper part of the thorax, because 

 here the relative difference in the length of the ribs is greatest. Hoover 

 attributes a certain diagnostic significance to loss of the undulatory 

 movement, diminution in the extensibility of the underlying lungs causing 

 it to become less or to disappear. The phenomenon is elicited by placing 

 the tip of the ring finger on the second rib in the midclavicular line, the 

 tip of the middle finger on the third rib midway between the midclavicu- 

 lar and anteroaxillary line, and the tip of the index finger on the fourth 

 rib in the midaxillary line. The patient is then instructed to make a 

 moderately rapid and deep inspiration. The finger on the third rib will 

 be observed to move farther than that on the second rib, and the finger 

 on the fourth rib will move farther than that on the third. The move- 

 ment of each rib from above downward succeeds and exceeds that in 

 the rib just above. 



When there is a moderate degree of impairment in the ventilation of 

 the upper lobe, the three ribs move in unison and through the same dis- 

 tance, so that the undulatory movement is lost although the ribs involved 

 may exhibit a considerable excursion. The undulatory movement is also 

 impaired by any disease which encroaches on the air spaces, invades the 

 interstitial tissue of the lung, or displaces the lung as in the case of an 

 enlarged heart or a distended pericardial sac. Another possible factor 

 in this phenomenon is that any inflammatory process in the lung or ad- 

 jacent tissue will produce a reflex inhibition of the muscles of the ribs, 

 and thus limit the expansion of the thorax. 



The axis of movement of the lower ribs, as of the upper ribs, accurately 

 corresponds with that indicated by their articulation with the vertebrae, 

 because the muscles attached to them, as well as the diaphragm, influence 

 their movements to a large extent. Anteriorly the lower ribs from the 



