This section is from the book "Anatomy Of The Arteries Of The Human Body", by John Hatch Power. Also available from Amazon: Anatomy of the Arteries of the Human Body, with the Descriptive Anatomy of the Heart.
In addition to the three usual branches, the left vertebral, and the right internal mammary, or the left vertebral and right inferior thyroid, may be found arising from the arch; or there may be the three usual branches with two vertebrals, one on either side of the left carotid.
The subclavians and carotids may arise separately from the arch, with a common trunk for the left vertebral and inferior thyroid; or with a right inferior thyroid artery; or with a left vertebral, in which case the right subclavian may be either the first or last branch.
I shall have occasion, hereafter, to notice particularly a very remarkable case which I observed in the Carmichael or Richmond Hospital School, in which five branches arose from the arch, in consequence of the subclavian and external and internal carotids of the right side coming off separately from the aorta.