On Respiration 195 



Nor should it be overlooked that the cartilages, by 

 the interposition of which the ribs are joined to the 

 sternum, are inserted into the ribs with very notable 

 obliquity, as is shown in Plate II., Fig. 3, in which «, c, 

 is a rib, c, ^, the cartilage, by means of which the rib 

 is united to the sternum, ^, the angle formed by the 

 junction of the two. The obliquity, moreover, has for 

 its object that the ribs may be extended and drawn 

 outwards, circularly. 



It is, besides, to be noted that in inspiration, 

 especially when violent, the extremities of the false 

 ribs move a little inwards ; and the reason is that the 

 diaphragm is joined to both ends of the false ribs, 

 with the result that when it contracts, those ends are 

 drawn inwards, but when it is relaxed they rise to 

 their natural position. 



With regard to the serrate, the longissimus dorsi^ 

 and t\\& pectoralis muscles, it is probable that they have 

 nothing to do with the expansion of the chest. For 

 if the hand be placed on these muscles when we 

 suddenly apply all our strength to dilate the thorax, 

 it will be found that they neither harden nor draw 

 together at all ; yet this would happen if these 

 muscles underwent contraction. 



Besides the aforesaid muscles, the diaphragm also 

 contributes to the expansion of the chest, and indeed 

 ordinary inspiration seems to be mainly caused by it. 

 In expiration the diaphragm being in diastole, and 

 released from constriction and in a flaccid condition, 

 is pushed upwards into the region of the thorax by 

 the stomach and the other viscera contained in the 

 abdomen ; whence it is that it compresses the lungs 

 and diminishes the space in the chest. But in 

 inspiration the diaphragm is in systole, and con- 

 tracted, so that it no longer remains greatly curved 



