62 ANATOMY FOR NURSES. [Chap. VI 



winds around and finally terminates in a flat tendon, which is 

 inserted into the front of the humerus just below its head. 



These muscles cover nearly the whole of the back; but as they 

 act upon the bones of the upper extremity, they are often more 

 properly reckoned as belonging to the muscles of that region. 



The muscles of the thorax are chiefly concerned with the 

 movements of the ribs during respiration. They are the inter- 

 costals, subcostals, etc. 



The chief bulk of the anterior muscular wall of the chest is 

 made up of the pectoral muscles, the larger of which arises partly 

 from the front of the sternum. The fibres converging form 

 a thick mass, which is inserted by a tendon of considerable 

 breadth into the upper part of the humerus. As these muscles 

 move the arm, they are, like the superficial muscles of the back, 

 usually reckoned among the muscles of the upper extremity. 

 Covering the pectoral muscles is a superficial fascia (composed 

 of connective tissue) in which are lodged the mammary glands 

 and a variable amount of fat. 



The muscular walls of the abdomen are mainly formed by 

 three layers of muscles, the fibres of which run in different 

 directions, those of the superficial and middle layers being 

 oblique, and those of the innermost layer being transverse. In 

 the front of the abdomen these three layers of muscles are 

 replaced by tendinous expansions or aponeuroses, which meet in 

 the middle line, the line of union giving rise to a white cord- 

 like line, the linea alba. On each side of this line the fibres of 

 a straight muscle, the rectus muscle, extend in a vertical direc- 

 tion between the tendinous layers. The abdominal muscles 

 are covered and lined by sheets of fascise, some of which are 

 very dense and strong, and serve to strengthen weak points in 

 the muscular walls. 



The strongest and most superficial of the abdominal muscles 

 is the external oblique, the fibres of which, arising from the lower 

 eight ribs, incline downwards and forwards and terminate in the 

 broad aponeurosis, which, meeting its fellow of the opposite side 

 in the linea alba, covers the whole of the front of the abdomen. 

 The lowest fibres of the aponeurosis are gathered together in 

 the shape of a thickened band, which extends from the anterior 

 superior spinous process of the ilium to the pubic bone, and 

 forms the well-known and important landmark, called from the 



