310 A Composite Study of the Subclavian Artery in Man 



1st to the 7th, most frequently the (ith, and most infrequently the 7th. 

 He also mentions a double vertebral artery, one arising from the inferior 

 thyroid artery, the other from the subclavian, uniting at the 4th cervical 

 vertebra. Quain gives a chart of a similar double vertebral artery. 



The internal mammary artery arises alone from Part I in 80% of the 

 cases, and is associated with other arteries by origin in a common trunk in 

 20% of the cases, arising with the thyroid axis in 10% of the latter, with 

 the suprascapular in 10% of them, and with tlic transverse cervical and 

 suprascapular once. The distribution of the artery is worked out in 

 minute detail only 28 times. A lateral tlioracic artery is found five 

 times in the 28. It is as large as the internal mammary, is derived from 

 the latter close to its origin from the subclavian, and passes between the 

 parietal pleura and the ribs along the anterior axillary line, sending 

 branches into the intercostal spaces from the 1st to the 9th, and losing 

 itself in one of these spaces or in the diaphragm. A lateral thoracic 

 artery is mentioned by Quain, Tiedemann, Henle, and other anatomists, 

 but is given as a very rare anomaly. Intercostal branches come from 

 the internal mammary as single arteries posterior to the intercostal 

 spaces, sending one branch to the superior part and another to the in- 

 ferior part of the spaces; or they arise posterior to the costal cartilages, 

 sending a branch above and one below the adjoining rib ; or there are two 

 intercostal branches to each space, one below the rib above it, the other 

 above the rib below it. Any two or all three of these arrangements may 

 be found on one side of a subject. In 54% of the subjects there are 

 two branches to each intercostal space, in 46% only one. 



The thyroid axis' is found as shown in Type I, Fig. 2, in 30% of the 

 cases, 22% of these being on the right side of the body, and 8% on the 

 left side. It is present as shown in Type II, Fig. 3, in 27% of the cases, 

 22% of these being on the left side of the body, and 5% on the right side. 

 Quain and Gray give Type II as normal. Tiedemann, Henle, Gegenbaur, 

 Sappey, Testut and other French and Grcrman anatomists give Type I as 

 the most frequent. 



The inferior thyroid artery^ arises as shown in Type I in 35% of the 

 subjects; it arises from Part I as a single branch in 33% of the subjects, 

 and as shown in Type II, in 32% of the subjects. 



The suprascapular artery" arises as shown in Type I in 3G% of the 

 subjects; in Type II in 34%, and from the subclavian alone as a single 

 branch in 30% of them. 



This artery is absent 4 times, double 3 times, and very small 4 times. 

 The long thoracic artery arises from it once. 



* Table 2, p. 318. = Table 3, p. 318. "Table 5, p. 319. 



