SUBCLAVIAN, AND ITS BRANCHES. 209 



from its origin; this imparts some advantage to the current of 

 the blood. 



2. The Inferior Thyroid Artery (Jlrteria Thyroidea Inferior) 

 arises from the upper face of the subclavian, and goes to the 

 thyroid gland. It ascends at first on the internal margin of the 

 scalenus medius muscle, and then turns suddenly inwards be- 

 tween the vertebrae and the great vessels of the neck. 



In this course several unimportant twigs are sent from it to 

 the contiguous parts. Near its root it detaches the Anterior, 

 or the Ascending Cervical Artery, which going up the neck is 

 spent upon the head of the muscles arising from the transverse 

 processes, as the scaleni, the longus colli, and so on. The infe- 

 rior thyroidal then gets to the thyroid gland, and is very mi- 

 nutely distributed to it, anastomosing with the other arteries 

 which supply the same organ. 



3. The Superior Intercostal Artery, (Jlrteria Intercostalis 

 Superior,) arising from the under surface of the subclavian op- 

 posite the inferior thyroid, descends across the neck of the first 

 rib, and divides into two branches, which supply the two upper 

 intercostal spaces: each of them also sends backwards near the 

 vertebra a small trunk to the rrruscles of the back. 



4. The Internal Mammary Artery (Jlrteria Mammaria In- 

 terna, Tkoracicd) descends at first along the internal margin of 

 the scalenus anticus; having then got fairly into the cavity of 

 the thorax, it continues to descend across the posterior face of 

 the costal cartilages, parallel with, and about nine lines from, 

 the outer edge of the sternum, between the triangularis sterni 

 and the intercostal muscles. 



In this course, besides some distinct twigs to the anterior me- 

 diastinum, it sends a branch (Phrenica Superior) which accom- 

 panying the phrenic nerve between the pleura and the pericar- 

 dium, reaches finally the diaphragm, and is spent upon it. At 

 each intercostal space which it crosses, the internal mammary 

 sends outwards a branch, which is spent upon the fore part of 

 the intercostal muscles, and anastomoses with the correspond- 

 ing intercostal artery : other branches also leave it at each space. 



