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TEXT-BOOK OF PHYSIOLOGY. 



originally by Bernouilli, which consists, as shown in Fig. 171, of a 

 vertical support carrying two freely movable parallel bars united at 

 their outer extremities by a short vertical strip, representing respec- 

 tively the vertebral column, two adjoining ribs, and a piece of the 



sternum. The paral- 

 lel bars are joined to 

 each other by a short 

 elastic band having 

 the direction of and 

 representing the ex- 

 ternal intercostal mus- 

 cles. If the bars are 

 depressed, the elastic 

 band is elongated and 

 made tense. On re- 

 leasing the bars the 

 band at once recoils 

 and elevates them. 

 Although the elastic 

 force is the same in 

 both directions, the 

 bars are yet elevated 

 for the reason that 

 in accordance with 

 the parallelogram of 

 forces the component 

 acting upward on the 

 long arm of the lever 

 preponderates over 

 the component acting 

 downward on the 

 short arm of the 

 lever. The action of 

 the band is supposed 

 to disclose and illus- 

 trate the action of the 

 muscle. 



The intercartilagi- 

 nei, those portions of 

 the intercostales in- 

 terni which occupy 



5 space between the costal cartilages from the sternum to their outer 

 extremity, bear the same relation to the cartilages in reference to the 

 sternum that the external intercostals bear to the ribs in reference to 

 the vertebral column; that is, the point of attachment to the cartilage 



FIG. 170. SHOWING THE SITUATION, THE POINTS OF 

 ATTACHMENT, AND DIRECTION OF THE INTER- 

 COSTAL MUSCLES, i. The intercostales extern!. 

 2. The intercostales interni. 3. The intercarti- 

 lagmei. (Deaver.) 



