324 MUSCLES OF THE THORAX. 



3. Serratus Magnus, 



Arises from the nine superior ribs, by an equal number of 

 fleshy digitations, resembling the teeth of a saw. 



Inserted, fleshy, into the whole base of the scapula internally, 

 between the insertion of the rhomboid and the origin of the 

 subscapularis muscle, being folded about the two angles of the 

 scapula. 



Use. To move the scapula forwards : and, when the scapula 

 is forcibly raised, to draw upwards the ribs. 



Muscles situated between the Ribs, and ivithin the Thorax. 



Between the ribs, on each side, there are eleven double rows 

 of muscles, which are, therefore, named intercostals. These 

 decussate each other like the strokes of the letter X. 



1 . Intercostales Kxterni, 



Arise from the inferior acute edge of each superior rib, and 

 run obliquely forwards, the whole length from the spine to 

 near the joining of tlie ribs with their cartilages ; from which, 

 to the sternum, there is only a thin membrane covering the 

 jnternal intercostals. 



Inserted into the upper obtuse edge of each inferior rib, as 

 ar back as the spine, into which the posterior portion is fixed. 



2. Intercostales Interni, 



Arise in the same manner as the external : but they begin at 

 the sternum, and run obliquely backwards, as far as the angle 

 of the rib ; and from that to the spine they are wanting. 



Inserted in the same manner, as the external. 



Use. By means of these muscles, the ribs are equally raised 

 upwards, during inspiration. Their fibres being oblique, give 

 them a greater power of bringing the ribs near each other, than 

 could be performed by straight ones. By the obliquity of 

 the fibres, they are almost brought contiguous : and as the fixed 

 points of the ribs are before and behind, if the external had 

 been continued forwards to the sternum, and the internal 



