126 KESPIKATION RESPIRATORY MOVEMENTS. 



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. 



Transversals. The expiratory action of this muscle is mainly in com- 

 pressing the abdominal 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 downward, acting as an antagonist to the 

 lower levatores costarum. 



There are some other muscles which 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, al- 

 though all the muscles which have been classed as ordinary inspiratory mus- 

 cles 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 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 less than three years of 

 age, irrespective of sex, respiration being carried on almost exclusively by the 

 diaphragm. 



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

 the sexes is observed. In the male the abdominal conjoined with the inferior 

 costal type is predominant, and this continues through life. In the female 

 the inferior costal type is insignificant and the superior costal type predom- 

 inates. Without discussing the question as to the exact age when this differ- 

 ence in the sexes first makes its appearance, it may be stated in general 

 terms, that a short time before the age of puberty in the female, the superior 

 costal type becomes more marked and soon predominates. In the male, 

 respiration continues to be carried on mainly by the diaphragm and the 

 lower part of the chest. 



The cause of the pronounced movements of the upper part of the chest in 

 the female has been the subject of considerable discussion. It is probably due, 

 in a great measure, to the mode of dress now so general in civilized countries, 

 which confines the lower part of the chest and renders movements of expan- 

 sion somewhat difficult. In a series of observations by Thomas J. Mays 

 (1887), upon eighty-two chests of Indian girls at the Lincoln Institution in 



