OF THE THORAX 



419 



ities of the transverse processes of the seventh cervical and the eleven upper 

 thoracic vertebrae. They pass obliquely downward and outward and are inserted 

 into the upper border, between the tubercle and the angle, of the rib, immediately 

 below its vertebras of origin. Each of the Inferior levatores divides into two 

 fasciculi, one of which is inserted as above described; the other fasciculus passes 

 down to the second rib below its origin; thus, each of the lower ribs receives 

 fibres from the transverse processes of two vertebras. 



Nerves. The muscles of this group are supplied by the intercostal^ nerves. 



STEHNOMASTOID. 



SUBCLAVIUS 



SUBCLAVIUS. 



Internal mam- 

 mary artery. 



,TRIANGULARIS 

 STERNI. 



FIG. 314. Posterior surface of sternum and costal cartilages, showing Triangularis stern! muscle. (From a 

 preparation in the Museum of the Royal College of Surgeons of Kngland.) 



The Diaphragm (diaphragma) (Figs. 315 and 316) is a thin, musculofibrous 

 septum placed at the junction of the upper with the middle third of the trunk; 

 it separates the thoracic from the abdominal cavity, its convex upper surface 

 forming the floor of the former, and its concave under surface the roof of the 

 latter. Its peripheral part consists of muscle fibres which arise from the internal 

 circumference of the thoracic outlet, as well as from certain lumbar vertebrae, 

 and pass upward and inward to converge to a central tendon. Anteriorly, the 

 Diaphragm arises from the dorsal surface of the ensiform cartilage by two fleshy 

 strips (pars sternalis); on either side, from the inner surfaces of the six lower 

 costal cartilages (seventh to twelfth) (pars costalis), interdigitating with slips of 

 origin of the Transversalis abdominis. Behind, it takes origin from certain 



