There are two subclavian arteries, both of which are tributaries off of the aorta in the chest. There are normally distinguished, however, by the fact that they are not symmetric. The L. subclavian comes directly off of the aortic arch, whereas the R. subclavian comes off of the brachiocephalic artery (which comes off of the aortic arch). The brachiocephalic splits, in essence, into the R. carotid artery and the R. subclavian. Here's a nice diagram (see the bottom picture, not the top two):
http://connection.lww.com/Products/sadler/images/figurelarge11-34.jpg
An "aberrant" R. subclavian is relatively common, occuring in 1 of 200 people. In most people it occurs without any symptoms, but in some individuals it can lead to a problem. The artery, although it supplies the R. upper extremity actually arises, in this instance, in the L shoulder region. Then it has to cross the chest to reach its destination, and in so doing, it can put pressure on the esophagus or trachea and cause eating or breathing problems. This is usually detected at a young age in those who will develop any symptoms at all.
I hope that this has helped. Take care
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