A CCESSOR Y RESPIRA TOR Y MO VEMENTS. 2 7 9 



and E. du Bois-Ileymond, 1 who, while accepting Martin and Hartwell's 

 view with regard to the intercostals between the bones, show conclusively 

 that the intercartilaginous muscles contract synchronously with the dia- 

 phragm, and are therefore, as Hamberger thought, inspiratory. The 

 method they employed was practically identical with that devised by 

 Martin. In normal respiration, the contraction of these muscles was 

 not noticeable ; it only became evident in laboured respiration. 2 After 

 apnoea has been produced, the intercartilaginous muscles begin to con- 

 tract later than the diaphragm. Division of the phrenic nerve has no 

 influence on their contractions. 



Expiration. — The diminution of the thoracic cavity which gives rise 

 to expiration is under normal conditions not associated with the active 

 contraction of any muscles. As the inspiratory muscles relax, the lung, 

 in virtue of its elasticity, tends to contract and drag the chest wall 

 with it. Moreover, the ribs which have been raised against gravity 

 and the elastic resistance of the rib cartilages, return to their previous 

 condition, while the slack diaphragm is pushed up into the chest by the 

 retraction of the abdominal walls pressing upon the abdominal viscera. 



Laboured respiration — In forced inspiration, such as occurs when 

 there is any obstruction to the entrance of air into the lungs, or if the 

 aeration of the blood be prevented in any way, in addition to a more 

 powerful action of the muscles already mentioned, the aid of other muscles 

 is called in. In order to secure an inspiratory action of these accessory 

 muscles, a fixed attachment must be provided by the elevation and 

 support of the head, shoulder, and arm. The chief of these accessory 

 muscles are the sterno-mastoid, the pectoralis minor, the lower part of 

 the pectoralis major, and the lower slips of the serratus magnus. 



The chief muscles concerned in forced expiration are those forming 

 the abdominal wall. These press on the contents of the abdomen and 

 pull down the sternum and ribs, thus diminishing the cavity of the 

 thorax in all directions. They are assisted in the depression of the 

 lower ribs by the serratus posticus inferior and portions of the sacro- 

 lumbalis. In the strong expiratory convulsions of asphyxia, an enormous 

 number of muscles come into play, and every muscle which can depress 

 the ribs or press on the abdominal viscera, or afford a fixed point for 

 muscles having these actions, is forcibly contracted. 



Accessory respiratory movements. — Besides the movements of the 

 thorax which bring about changes in the capacity of this cavity, and so 

 serve to draw air into, or expel air from, the lungs, certain other move- 

 ments are connected with the respiratory act, known as accessory or 

 concomitant respiratory movements. These have no influence on the 

 size of the thoracic cavity, but serve simply to facilitate the entrance 

 and exit of air to and from the lungs. Many of them are wanting in 

 normal respiration, and are only seen when the breathing becomes 

 laboured from any cause. 



1. Movements of the larynx. — Even in quiet respiration there is a 

 movement of the larynx up and down, the upward movement correspond- 

 ing to expiration. The depression of the larynx during inspiration is 

 due partly to contraction of the sterno-hyoid and sterno-thyroid muscles, 



1 Arch.f. Physiol., Leipzig, 1896, S. 85. 



- Weidenfeld, Sitzungsb. d. /r. Akad. d. Wissensch., Wien, 1894 (3), Bd. ciii., had per- 

 sonally come to the conclusion, from his experiments, that the intercostals take no part in 

 the respiratory movements. 



