THE MUSCLES AND FASCIAE OF THE TRUNK 139 



of the posterior border of the clavicle (collar bone); 

 middle fibers horizontally to inner margin of acromion 

 and superior lip of spine of scapula; inferior fibers 

 terminate in a triangular aponeurosis, which glides 

 over a smooth surface at the inner extremity of the 

 spine to be inserted into a tubercle at the outer portion 

 of this surface. 



Latissimus Dorsi. This is one of the largest and 

 longest muscles in the body. Broad and flat at its 

 origin, narrow at its insertion, it covers the lumbar 

 region of the back and the lower half of the thoracic 

 region. Origin, spinous processes of the lower six 

 or seven thoracic vertebrse, posterior layer of lumbar 

 aponeurosis which attaches it to the lumbar and sacral 

 spines, and supraspinous ligament, from the outer lip 

 of the iliac crest, also arises by three or four fleshy slips 

 from three or four lower ribs. Its upper fibers pass 

 horizontally outward, the middle obliquely upward, 

 and the lower fibers vertically upward, they become 

 narrowed into a tendon, 1J inches wide, which passes 

 back of the arm-pit (axilla) in front of the teres major 

 muscle, to be inserted into the bicipital groove on the 

 anterior and upper aspect of the humerus (arm 

 bone). 



Actions. Depresses arm; draws it toward body 

 (adducts); turns it inward; acts in striking a blow 

 or chopping wood, etc.; when arms are firmly held 

 in position, it assists the chest and abdominal muscles 

 to suspend and draw forward or upward the whole 

 trunk, as in climbing, etc. Nerve subscapular from 

 brachial plexus. 



The Muscles of the Thorax 



External intercostals. Triangularis sterni. 



Internal intercostals. Levatores costarum. 



Infracostales (subcostales) . Diaphragm. 



