Muscles of the Chest. 



263 



Pars clavicularis 



Crista 

 tuborculi 

 majoris ~ 



Posterior 

 layer of the " 

 teniiiiia) 

 tfiidoii 



Anterior 

 layer of ttie 

 terminal 

 tendon 



Corpus 

 luiiiieri* 



Pars 

 steriiocostalis 



Part of the jnuscle which passes to the 

 posterior layer of the terminal tendon 



Pars abdominalis 



309. Right m. pectoralis major, 



semi - schematically. 



viewed from in front, 



(Two strips have been cut out of the muscle. The dotted black lines indicate the course of the upper, 

 posterior margins of the muscle bundles, the dotted red lines that of the lower, anterior margins.) 



M. pectoralis major (continued). Insertion: the fibers converge, lateralward to 

 the crista tuberculi majoris of the humerus. The fibers of the pars sternocostalis and of 

 the pars abdominahs pass, at the lower margin of the tendinous attachment, to the posterior 

 surface of the same and thence to the bone, without altering their direction, so that the fibers 

 which arise lowest down are inserted highest up ; the tendon of insertion , accordingly , looks 

 as though it were rolled up at its lower margin and consists of two layers, one anterior, thick 

 (formed chiefly by the pars clavicularis), and one posterior, thin (pertaining especially to the 

 pars sternocostalis and pars abdominalis) ; these layers are continuous below but can be separated 

 from above (see Fig. 310). Between the posterior surface of the terminal tendon and the 

 anterior surface of the caput longum m. bicipitis brachii there often lies an oblong bursal sack, 

 l)iirsa m. pectoralis majoris (see Fig. 346). Action: it draws the upper arm medianward 

 and forward, and rotates it inward. Innervation: nn. thoracales anteriores. 



