692 



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 cartikges, 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 intercostal 

 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 the chest is rarely enlarged at two 

 places at one and the same time. 



In conclusion the author conceives that he has established the 

 following propositions : — 



1st. Costal breathing may be distinguished from abdominal by 

 determining which part is first put in motion, and the kind of re- 

 spiration may be designated according to the name of such part. 



2nd. Healthy costal breathing begins with the motion of a supe- 

 rior rib, which is followed by that of the lower ones in succession. 



3rd. Ordinary respiration in men is abdominal, in women, costal ; 

 extraordinary breathing is the same in both sexes. 



4th. Any of the ribs, from the twelfth to the first, may carry on 

 respiration. 



5th. Diseased respiration is of various kinds ; the movements may 

 be symmetric or not symmetric, costal or abdominal; all or none of 

 the ribs may move; the abdomen may or may not move; the chest 



