The development of the brachial supports has been studied by Friele, Fischer and Oehlert.
Left brachial artery arising from a common innominate trunk, instead of coming off separately from the aortic arch.
In this development of brachial extensions of the theca the genital organs were involved, and their ripe products formed at the ends of the brachia or in the branches therefrom.
This causes tension on the brachial plexus which may stretch or rupture the nerves.
The brachial plexus is formed by four or five of the lowest cervical nerves; the last nerve of this plexus often marks the boundary of the cervical and thoracic vertebrae.