140 MUSCLE TISSUE 



The Intercostal Muscles. These are thin, flattened 

 muscles extending between the margins of two adjacent 

 ribs, filling the intervening spaces called intercostal. 

 These muscles are covered by the intercostal fascia, 

 internally and externally, and a layer lies between 

 the two muscles. 



The Subcostals. The subcostals (infracostals) or 

 muscles below the lower ribs consist of muscular and 

 aponeurotic fibers, which are attached to the inner 

 surface of one rib (usually lower ribs), and inserted 

 into the inner surfaces of the first, second, or third rib 

 below. They are placed on the parts of the ribs 

 where the internal intercostal muscles end posteriorly. 



The Triangularis Sterni. This is a thin, irregular- 

 shaped muscle found on the posterior surface of the 

 sternum (breast bone), and it passes to the costal 

 cartilages of the ribs from the second to sixth inclusive. 

 It is a single muscle. 



The Levatores Costarum (Elevators of the Ribs) . These 

 are twelve in number found on each side of the verte- 

 bral column external to the thoracic cavity. Origin, 

 by small tendinous and fleshy bundles from the ex- 

 tremities of the transverse processes of the seventh 

 cervical and the eleven upper thoracic vertebrae; pass 

 obliquely downward and outward to be inserted into 

 the upper border, between the angle and tubercle of 

 the rib, immediately below its vertebra of origin. 

 Each of the lower elevator muscles divides into two 

 slips, one of which is inserted as described above 

 the other slip passes to the second rib below its origin; 

 thus each of the lower ribs receives fibers from two 

 vertebrae. 



Diaphragm. This is a musculofibrous wall which 

 divides the thoracic and abdominal cavities. It is 

 dome-shaped; the convex, upper surface forms the 

 floor of the thoracic cavity, and the concave lower 

 surface the roof of the abdominal cavity. The attach- 

 ments of the diaphragm are as follows: In front the 



