106 RESPIRATION 



pressing the abdominal viscera against the diaphragm. Acting from 

 its attachments to the linea alba, the crest of the ileum and Poupart's 

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

 downward. 



Obliquus Intermix. This muscle also acts in forced expiration by 

 compressing the abdominal 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 attach- 

 ments to the cartilages of the four inferior ribs, it draws them down- 

 ward. 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 exerted 

 mainly in compressing the abdominal viscera. 



Sacro-lnmbalis. 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 downward, acting as an 

 antagonist to the lower levatores costarum. 



There are other muscles that may be used in forced expiration, 

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

 inferior, the superior fibres of the serratus magnus and the inferior 

 portion of the trapezius ; but their action in respiration is unimportant. 



Types of Respiration. In the movements of expansion of the chest, 

 although all the muscles that 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. Three types 

 usually are 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 

 that 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 

 that dilate the thorax above the seventh rib and elevate the entire 

 chest is most prominent. 



The abdominal type is most marked in children less than three years 

 of age, irrespective of sex, respiration being carried on almost exclu- 

 sively by the diaphragm. 



At a variable period after birth, a difference in the types of respira- 

 tion in the sexes is observed. In the male the abdominal conjoined 



