388 KESPIRATION. 



opposed more or less by the diaphragm, by which means the 

 duration or intensity of the expiratory act is regulated. 

 They are also attached to the ribs or costal cartilages, and 

 while they press up the diaphragm, 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 action 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 after violent exercise, the auxiliary muscles of ex- 

 piration, as well as of inspiration, are called into action to a 

 considerable extent; 



Obliquus Externus. This muscle, in connection with the 

 obliquus internus and transversalis, is efficient in forced or 

 labored expiration, by pressing the abdominal viscera 

 against the diaphragm. Its fibres run obliquely from above 

 downwards and forwards. Acting from its attachments to 

 the linea alba, crest of .the ileum, and Poupart's ligament, by 

 its attachment to the eight inferior ribs, it draws the ribs 

 downwards. 



Obliquus Internus. This muscle also acts in forced expi- 

 ration by compressing the abdominal viscera. The direction 

 of its fibres is from below upwards and forwards. Acting 

 from its attachments to the crest of the ileum, Poupart's lig- 

 ament, and the lumbar fascia, by its attachments to the carti- 

 lages of the four inferior ribs, it draws them downwards. 

 The direction of the fibres of this muscle is the same as that 

 of the internal intercostals. By its action the ribs are drawn 

 inwards as well as downwards. 



Transversalis. The expiratory action of this muscle is 

 mainly in compressing the abdominal viscera. 



