INSPIRA TION. 2 7 7 



sponding to the costal origins of this muscle. This groove is frequently 

 seen in rickety children, where the softness of the bones has been com- 

 bined with respiratory troubles. 



The contraction of the diaphragm may also cause a widening of the 

 lower part of the thorax, since in its descent it presses upon the abdominal 

 viscera, so distending the abdomen and pushing out the lower ribs. 



The elevation of the ribs in respiration is carried out by means of 

 the contraction of a number of muscles, of which the external inter- 

 costals are usually regarded as the most important. Other muscles 

 involved in the act are the scalenus anticus, the serratus posticus 

 superior, and the levatores costarum. Whereas these muscles raise the 

 upper ribs towards the spinal column and fix it in this elevated position, 

 the external intercostals raise all the ribs with the exception of the first, 

 each intercostal acting from its attachment to the rib above as a fixed 

 point. 



The functions of the external and internal intercostal muscles have 

 been the subject of considerable discussion ever since Hamberger l put 

 forward his views concerning these muscles, and the question cannot 

 even yet be regarded as finally decided. 



In discussing the action of the intercostal muscles, we must dis- 

 tinguish three portions — 



1. The external intercostal muscles, which run from one rib to the 

 next rib below in an oblique direction, for- 

 wards and downwards. They extend from 

 the levatores costarum behind to the rib 

 cartilages in front. 



2. The internal intercostal muscles, which 

 extend from the angles of the ribs behind to 

 the rib cartilages in front. The fibres are 

 directed downwards and backwards, and are 

 somewhat shorter and less oblique than those 

 of the external intercostals. 



3. The musculi intercartilaginei, which are 



generally regarded by anatomists as part of the internal intercostals, their 

 fibres being directed, like those of the latter, downwards and outwards. 



With regard to the actions of the external muscles, most physio- 

 logists 2 have accepted the view put forward by Hamberger, that they 

 are inspiratory in function, and that their action is to raise the ribs. 

 Hamberger founded his theory on the following geometrical considera- 

 tions. If in the Fig. 165 ac and bd represent two ribs, which can rotate 

 in a vertical direction about two points a and b, and cd represent the 

 sternum, then abed represents a parallelogram, of which only one side 

 ab is fixed. The line ef corresponds in direction to a fibre of the 

 external intercostal muscles. The force with which this fibre tends to 

 move the two ribs may be represented by the lines he and gf. Of 

 these he represents the force acting at the point e, and tending to 

 depress the rib ac, while fg represents the force acting at /, and tend- 

 ing to raise the rib bd. Since the component acting in an upward 



1 " De Respirationis mechanismo" (quoted from Rosenthal, Hermann's "Handbuch, 

 Bd. iv. S. 189). 



2 Hutchinson, Todd's "Cyclopaedia," London, 1852, vol. iv. p. 1043; Volkmann, 

 ZUrhr. /'. Anat. u. Enticeklngs., Leipzig, Bd. ii. S. lf>9 (quoted from Rosenthal); New. 'II 

 Martin, Juurn. Physiol., Cambridge and London, 1879, vol. ii. p. 24. 



