MUSCLES OF THE THORAX. 323 



Muscles situated on the Anterior Fart of the Thorax. 



These may be divided into two layers. The first layer con- 

 sists of one muscle, named 



Pectoralis Major, 



Arises from the cartilaginous extremities of the fifth and 

 sixth ribs, where it always intermixes with the external 

 oblique muscle of the abdomen ; from almost the whole length 

 of the sternum : and from near half of the anterior part of the 

 clavicle ; the fibres run towards the axilla in a folding manner. 



Inserted, by two broad tendons, which cross each other at 

 the upper and inner part of the os humeri, above the insertion 

 of the deltoid muscle, and outer side of the groove for lodging 

 the tendon of the long head of the biceps. 



Use. To move the arm forwards, and obliquely upwards, 

 towards the sternum. 



The second layer consists of three muscles. 



1 . Subclavius, 



Arises, tendinous, from the cartilage that joins the first rib to 

 the sternum. 



Inserted, after becoming fleshy, into the inferior part of the 



clavicle, wiiich it occupies from within an inch of the sternum, 



as far outwards as to its connexion, by ligament, with the 

 coracoid process of the scapula. 



Use. To pull the clavicle downwards and forwards. 



2. Pectoralis Minor, 



Arises, tendinous and fleshy, from the upper edge of the 

 third, fourth, and fifth ribs, near where they join with their 

 cartilages. 



Inserted, tendinous, into the coracoid process of the scapula : 

 but soon grows fleshy and broad. 



Use. To bring the scapula forwards and downwards, or to 

 raise the ribs upwards. 



