Royal Society, 223 



After premising an account of the views of several eminent phy- 

 siologists, and in particular those promulgated by Haller, the author 

 shows that they resolve themselves into the general opinion that the 

 scalene or other muscles of the neck fix the first rib, in order to 

 enable the two sets of inlei'costal muscles to act either separately or 

 conjointly, as inspiratory or expiratory muscles. He then proceeds 

 to state the proofs that the intercostal muscles possess an action 

 which is independent of any other muscle, and also independent of 

 each other, so that any of the twelve ribs may be elevated or de- 

 pressed by them either separately or conjointly. He demonstrates 

 the nature of this action by means of models, producing oblique 

 tensions betweeti levers representing the ribs, and allowing of rota- 

 tion on their centres of motion ; and he shows that such tension in 

 the direction of the external intercostal muscles, elevates both the 

 levers until the' tension ceases, or the position of the bars by proxi- 

 mity obstruct each other. If the tension be exerted in a contrary 

 direction, as in the internal intercostal muscles, the bars are both 

 depressed. This movement was demonstrated by a model. It was 

 farther shown that two tensions decussating can, according to the 

 position of the fulcra, be made to act as associates or antagonists to 

 each other. Such motions are to be considered with reference to 

 the fulcra, bars with one fulcrum common to each having no such 

 action ; and the author accordingly draws the following conclu- 

 sions : — 



1st. All the external intercostal muscles are true inspiratory mus- 

 cles, elevators of the ribs, and with this act they dilate the inter- 

 costal spaces, thus increasing the cavity of the chest. 



2nd. The internal intercostal muscles have a double action; the 

 portions situated between the cartilages are associates in action 

 with the external layer, and act as elevators of the cartilages, while 

 the portion between the ribs are depressors, or antagonists of the 

 external layer, and are here true expiratory muscles ; with this they 

 decrease the intercostal spaces. 



3rd. These muscles can elevate or depress the ribs independently 

 of any other muscle, fixing the first or last rib. Any one lamella, 

 or series of muscles, can, as required, independently perform in- 

 spiration or expiration at any one of the twenty-two intercofctal 

 spaces. 



4th. In inspiration, the intercostal spaces increase, with a short- 

 ening of the muscle ; and in expiration, they decrease their perpen- 

 dicular distance, with a shortening of the muscle. 



5th. All parallel intercostal muscles, acting with uniform force, 

 concur in the same effect, whether near the fulcrum or more distant 

 from it, and these muscles gain power with their increasing obliquity 

 as well as speed. 



In the third part of the paper an account is given of the differ- 

 ence between the external thoracic space and the internal pulmonic 

 space. The respiratory movements are described in health and 

 disease, and it is shown that tiie chest is rarely enlarged at two 

 places at one and the 9ame time. 



