DISTRIBUTION OF THE ARTERIES. 97 



neck, has a similar division at the os-hyoides, into exter- 

 nal and internal carotids, supplies with a like number of 

 branches the left upper half of the neck, face, side and 

 posterior parts of the head; while the left internal carotid 

 supplies the left half of the brain. 



The whole number of branches,, of any magnitude, which 

 belong to the carotids upon both sides of the neck, are about 

 22; 16 of this number going to the upper neck and exterior 

 head, while the remaining supply the brain. 



The subclavian artery, having its origin on the right side 

 from the arteria innominata, and on the left from the arch 

 of the aorta proceeds in the first stage of its course to the 

 scaleni muscles, between the anterior and middle of which 

 it passes. It then proceeds between the clavicle and first 

 rib to the tendons of the latissimus dorsi and teres major 

 muscles, over which it passes, completing the second stage 

 of its course. We now follow it down the arm along the 

 inner edge of the biceps muscle, upon the brachialis anticus 

 to a little below the elbow joint, forming its third and last 

 stage, where it divides into the radial and ulnar arteries, 

 which supply the forearm and hand. These three stages 

 have received distinct names the first stage is called the 

 subclavian, the second the axillary, the third the humeral. 

 Five branches belong to the first, eight to the second, and 

 six to the third stage. The whole number of primary 

 branches belonging to the two subclavian arteries, which 

 supply the upper extremities, is about 38. 



The chest and its organs are next in order as we pro- 

 ceed down the body and follow the course of the arterial 

 trunk. 



The aorta having made its curve, gives off the bronchial 

 arteries to the lungs; the oesophageal branches, five or 

 six in number, to the oesophagus; posterior mediastinal 

 branches, as the name imports, to the mediastinum; and 

 ten intercostal branches to the intercostal spaces and walls 

 of the chest the two upper intercostal spaces being sup- 

 plied from the subclavian. These arteries being all in 

 pairs, the whole number supplying the chest is about 40, 

 7 



