598 MUSCLES OF THE CHEST. 



terior surface of the sternum, the whole length of its two 

 upper bones, meeting its fellow tendon of the opposite side 

 along the median line, where they decussate, and thus 

 cover the sternum with a kind of aponeurosis. We have, 

 however, several times seen the sternal origin of this 

 muscle entirely fleshy, and meeting its fellow in the 

 same way along the median line. It also has a fleshy 

 origin from the fifth and sixth ribs, sometimes also from 

 the third and fourth, and a slip, sometimes fleshy and 

 sometimes aponeurotic, is seen to connect the lower portion 

 of the costal portion with the upper tendon of the external 

 oblique or rectus muscle. From these several origins the 

 fibres pursue different directions, the clavicular descend, the 

 sternal run horizontally, and the costal ascend the whole 

 uniting into one broad, thin tendon, which is inserted into 

 the anterior edge of the bicipital groove. At the axilla 

 the muscle is folded inward, presenting a thick, rounded 

 margin, and at its insertion the clavicular portion is seen 

 to descend lower than the sternal, thus producing a decus- 

 sation of its tendinous fibres. 



Function. To draw the arm inward and forward upon 

 the chest. If the arms be fixed, this muscle can elevate 

 the ribs, and thus aid in inspiration. If the arm be raised, 

 the costal portion can draw it down ; and by the action of 

 both muscles the arms are folded upon the chest. 



The Pectoralis Minor (Fig. 167) is triangular in shape, 

 and seen by raising the last from its origin, and turning 

 it over towards the humerus. It arises by thin tendin- 

 ous digitations from the third, fourth, and fifth ribs at 

 their superior margins, proceeds obliquely upward and 

 outward, and is inserted by a short, flat tendon into the 

 inner face of the coracoid process of the scapula. 



Function. To draw the shoulder inward, downward, t'nd 

 forward, and to assist the great pectoral in inspiration, by 

 raising the ribs, when the scapula and arm are fixed. 



Serratus Major Anticus, called also Serratus Magnus, (Fig- 

 193.) This muscle is distinctly brought to view by raising 

 both pectoral muscles, detaching the clavicle from thester- 



