148 HUMAN ANATOMY. 



MUSCLES OF THE THORAX. 



INTERCOSTALES EXTERNI. Eleven pairs on either side. 

 Origin, from the outer border of the groove on the lower border 

 of each rib, from the cartilage to the tubercle; insertion, into 

 upper border of the rib below; action, raises the ribs; nerve, 

 intercostal. 



INTERCOSTALES INTERNI. Origin, inner lip of the groove 

 on the lower border of each rib ; insertion, into the upper border 

 of the rib below; action, pulls the ribs upward; nerve, inter- 

 costal. 



FIG. 96. 



Diaphragm: 1, 2, 3, central cordiform tendon; 4, middle leaflet; 

 5, ligamentum arcuatum externum; 6, ligamentum arcuatum in- 

 ternum; 8, right crus; 10, left crus; 11, aortic opening; 12, oesopha- 

 geal opening; 13, opening for vena cava; 14, psoas magnus; 15, quadra- 

 tus lumborum. 



INFRACOSTALES (SUBCOSTALES). Origin, inner surface of 

 rib ; insertion, into the inner surface, from the first to the third 

 rib below; action, inspiratory muscles; nerve, intercostal. 



TRIANGULARIS STERNI. Origin, lower part of the back of 

 the sternum and back of ensiform cartilage and inner surface of 

 sternal end of the costal cartilages of the three or four lower 

 ribs ; insertion, into the border and inner surfaces of the costal 

 cartilages, from the second to the sixth rib inclusive (it is con- 

 tinuous below with transversalis ,abdominis muscle) ; action, 

 draws down the costal cartilages; nerve, intercostal. 



