MUSCLES OF THE THORAX. 



MUSCLES OP THE THORAX. 



The muscles of the thoracic ^vall are the intercostales, levatores cos- 

 tarum, subcostales, and triangularis sterni, and along with these the 

 diaphragm intervening between the thorax and abdomen may con- 

 veniently be grouped. 



The INTERCOSTAL MUSCLES consist of two thin layers of oblique short 

 muscular fibres filling up the intercostal spaces : these layers are named 

 respectively the external and internal muscles. 



Fiff. 219. 



Fio-. 219. — View of several op the jMiddle Dorsal Vertebr.e and Ribs, to show 

 THE Intercostal Muscles (after Cloquet). (A. T.) ^ 



A, from the side ; B, from behind. 



IV, the fourtli dorsal vertebra ; V, V, the fifth rib and its cartilage ; 1, 1, the levatores 

 costarum muscles, short and long ; 2, the external intercostal muscles ; 3, the internal 

 intercostal layer sliown, iu the lower of the two spaces represented, by tlie removal of the 

 external layer, and seen in A in the upper space, in front of the external layer : the 

 deficiency of the internal layer towards the vertebral column is shown iu B. 



The external intercostal muscles, consisting of muscular with 

 some tendinous fibres intermixed, are directed obHquely downwards 

 and forwards from one rib to another. Their extent for the most 

 part is from the tubercles of the ribs, nearly to the outer end of the 

 cartilages ; but in the two lowest intervals they reach forwards to the 

 ends of the spaces. Thin tendinous fibres, having the same direction 

 as the external intercostal muscles, are continued forwards between the 

 costal cartilages, from the points where the muscles cease, to the 

 sternum, and there cover the internal intercostals. 



The internal intercostal muscles, placed deeper than the preceding, 

 are attached to the inner margins of the ribs and their cartilages. 



