RESPIRATJOX. 



403 



ends are not free, and that the movement of rotation is materially different. 

 In fact, the mechanical conditions are so complex that deductions from phe- 

 nomena observed in such gross demonstrations or by means of geometric figures 

 such as suggested by Rosenthal and others must be accepted with caution. 



There is no doubt that stimulation of any of the intercostal fibres causes 

 an elevation of the rib below if the rib above be fixed, and that if the excita- 

 tion be sufficiently strong and the area be large, the effect may extend from rib 

 to rib, and thus a large part of the thoracic cage will be elevated. Conse- 

 quently, it has been assumed that, should the upper ribs be fixed, the contrac- 

 tions of both sets of intercostals would elevate the system of ribs below. But 

 the experiments of Martin and Hartwell l show that during forced inspiration 

 the internal intercostals contract alternately with the diaphragm and the exter- 

 nal intercostals, and therefore are expiratory. Moreover, Ebner 2 has found, 

 as a result of elaborate measurements, that the intercostal spaces, excepting the 

 first two, are, instead of being narrowed, actually widened during inspiration. 



Fig. 72. — Model to illustrate the action of the 

 external intercostals and interchondrals. 



Fig. 73.— Model to illustrate the action of the inter- 

 osseous portion of the internal intercostals. 



An examination of the origins and insertions of the external intercostals and 

 the interosseous portion of the internal intercostals, and of their actions during 

 contraction, renders it apparent that it is possible for the externi to elevate the 

 ribs and to widen the intercostal spaces, but that such effects are impossible in 

 the case of the interosseous portion of the internal intercostals. Thus, if we 

 take the model described above (Fig. 72), project a line a, 6 in imitation of 

 the relation of the external intercostals to the ribs, and raise the parallel bars 

 to a horizontal position, the distance between c, d is shorter than that between 

 a, l>. It is but a logical step from this demonstration to assume that, should a 

 strip of muscle be placed between «, b, the muscle in shortening would pull the 

 bars upward, at the same time widening the intercostal spaces. 1 1" now the 

 upper ribs be fixed, it is obvious that the external intercostals must raise the 

 ribs and open up the intercostal spaces during contraction. This same reason- 

 ing applies to the interchondrals, and the experiments of Hough 3 show that 

 they contract synchronously with the diaphragm, and therefore with the exter- 

 nal intercostals. 



1 Journal of Physiology, 1S79-80, vol. 2, p. 24. 2 Lnr. ril. 



3 Studies from the Biological Laboratory, Johns Hopkins University) March, 1894. 



