386 RESPIRATION. 



Auxiliaries. 



Muecle. Attachments. 



Obliquus Externus External surface and inferior borders of 



eight inferior ribs the anterior 



half of the crest of the ileum, Pou- 

 part's ligament, linea alba. 



Obliquus Internus Outer half of Poupart's ligament, ante- 

 rior two-thirds of the crest of the 



ileum, lumbar fascia cartilages of 



four inferior ribs, lineal alba, crest of 

 the pubis, pectineal line. 



Transversalis Outer third of Poupart's ligament, ante- 

 rior two-thirds of the crest of the 

 ileum, lumbar vertebrae, inner sur- 

 face of cartilages of six inferior ribs 



crest of the pubis, pectineal line, 



linea alba. 



Sacro-lumbalis Sacrum angles of the six inferior 



ribs. 



Internal Intercostals, The internal intercostals have dif- 

 ferent functions in different parts of the thorax. They are 

 attached to the inner borders of the ribs and costal cartilages. 

 Between the ribs they are covered by the external intercos- 

 tals, but between the costal cartilages are simply covered 

 by aponenrosis. Their direction is from above downwards 

 and backwards, at right angles to the external intercostals. 

 The function of that portion of the internal intercostals situ- 

 ated between the costal cartilages has already been noted. 

 They assist the external intercostals in elevating the ribs in 

 inspiration. Between the ribs these muscles are directly an- 

 tagonistic to the external intercostals. They are more nearly 

 at right angles to the ribs, particularly in that portion of the 

 thorax where the obliquity of the ribs is greatest. The ob- 

 servations of Sibson have shown that they are elongated 

 when the chest is distended, and shortened when the chest is 

 collapsed. This fact, taken in connection with experiments 

 on living animals, shows that they are muscles of expiration. 

 Their contraction tends to depress the ribs, and consequently 



