TYPES OF RESPIRATION. 131 



The above-mentioned muscles are called into action in ordinary tranquil respiration, 

 and their sole function is to diminish the capacity of the chest. In labored or difficult 

 expiration, and in the acts of blowing, phonation, etc., other muscles, which are called 

 auxiliaries, play a more or less important part. These muscles all enter into the forma- 

 tion of the walls of the abdomen, and their general action in expiration is to press the 

 abdominal viscera and diaphragm into the thorax and diminish its vertical diameter. 

 Their action is voluntary ; and, by an effort of the will, it may be opposed more or less 

 by the diaphragm, by which means the duration or intensity of the expiratory act is regu- 

 lated. They are also attached to the ribs or costal cartilages, and, while they press the 

 diaphragm upward, depress the ribs and thus diminish the antero-posterior and transverse 

 diameters of the chest. In this action, they may be opposed by the voluntary contraction 

 of the muscles which raise the ribs, also for the purpose of regulating the character of the 

 expiratory act. The importance of this kind of action in declamation, singing, blowing, 

 etc., is evident ; and the skill exhibited by vocalists and performers on wind instruments 

 shows how delicately this may be regulated by practice. 



In labored respiration in disease and in the hurried respiration which follows violent 

 exercise, the auxiliary muscles of expiration, as well as of inspiration, are called into 

 action to a considerable extent. 



Olliquus Externus. This muscle, in connection with the obliquus internus and trans- 

 versalis, is efficient in forced or labored expiration, by pressing the abdominal viscera 

 against the diaphragm. Its fibres run obliquely from above downward and forward. 

 Acting from its attachments to the linea alba, the crest of the ileum, and Poupart's liga- 

 ment, by its attachment to the eight inferior ribs, it draws the ribs downward. 



Obliquus Internus. This muscle also acts in forced expiration, by compressing the ab- 

 dominal viscera. The direction of its fibres is from below upward and forward. Acting 

 from its attachments to the crest of the ileum, Poupart's ligament, and the lumbar fascia, 

 by its attachments to the cartilages of the four inferior ribs, it draws them downward. 

 The direction of the fibres of this muscle is the same as that of the internal intercostals. 

 By its action the ribs are drawn inward as well as downward. 



Transversalis. The expiratory action of this muscle is mainly in compressing the ab- 

 dominal viscera. 



Sacro-lumbalis. This muscle is situated at the posterior portion of the abdomen and 

 thorax. Its fibres pass from its origin at the sacrum, upward and a little outward, to be 

 inserted into the six inferior ribs at their angles. In expiration it draws the ribs down- 

 ward, acting as an antagonist to the lower levatores costarum. 



There are some other muscles which may be brought into action in forced expiration, 

 assisting in the depression of the ribs, such as the serratus posticus inferior, the superior 

 fibres of the serratus magnus, the inferior portion of the trapezius, but their function is 

 unimportant. 



Types of Respiration. In the expansive movements of the chest, although all the 

 muscles which have been classed as ordinary inspiratory muscles are brought into action 

 to a greater or less extent, the fact that certain sets may act in a more marked manner 

 than others has led physiologists to recognize different types of respiration. The three 

 following types are generally given-in works on physiology : 



1. The Abdominal type. In this, the action of the diaphragm and the consequent 

 movements of the abdomen are most prominent. 



2. The Inferior Costal type. In this, the action of the muscles which expand the 

 lower part of the thorax, from the seventh rib inclusive, is most prominent. 



3. The Superior Costal type. In this, the action of the muscles which dilate the thorax 

 above the seventh rib and which elevate the entire chest is most prominent. 



The abdominal type is most marked in children under the age of three years, irrespec- 

 tive of sex. In them, respiration is carried on almost exclusively by the diaphragm. 



