ARTERIES. 



arch, just behind and to the left of the preceding, and run- 

 ning upward and slightly outward, this enters the neck oppo- 

 site the left sterno-clavicular joint. [801] 



Subclavian. The origin differs on the right and left sides. 

 It rises to a variable extent above the clavicle, sometimes to 

 the level of the lower border of the thyroid body. The Scalenus 

 anticus divides it in three parts. First part, left side : arising 

 from the arch behind and to the left of the carotid, this 

 ascends to the root of the neck and then arches upward and 

 outward to the border of the Scalenus anticus. First part, 

 right side : arising from the innominate, this runs to the border 

 of the Scalenus anticus. Second part (both sides) : this runs 

 outward behind the Scalenus anticus. Third part (both sides) : 

 this runs from the outer border of the Scalenus anticus to the 

 outer border of the first rib and there becomes the axillary. 

 The branches are the vertebral, thyroid axis, internal mam- 

 mary, and superior intercostal. The vertebral is the first branch, 

 arises from the upper and back part of the first part, and as- 

 cends in the neck. [82 1*] 



Thyroid Axis. Arising from the upper and front part of 

 the first part, close to the Scalenus anticus, this ascends and 

 soon divides into three branches, viz.: Inferior thyroid, as- 

 cending into the neck on the Scalenus anticus. Transverse 

 cervical, running backward in the neck to the Trapezius and 

 giving off muscular branches, the superficial cervical and the 

 posterior scapular. Suprascapular, running backward in the 

 neck to the suprascapular notch. [823] 



Internal Mammary. Arising from the under surface of 

 the first part, just below the preceding, this descends behind 

 the inner ends of the costal cartilages, lying on the pleura and 

 Triangularis sterni. At the sixth interspace it divides into the 

 musculo-phrenic and superior epigastric. Branches : Comes 

 nervi phrenici, accompanying the phrenic nerve. Mediastinal, 

 twigs to the anterior mediastinum. Pericardial, twigs to the 

 pericardium. Anterior intercostal, two branches to each of 



[131] 



