There is an axillary inlet (gateway to the upper limb) on each side of the superior thoracic aperture at the base of the neck (Fig. 8.11):
Structures such as blood vessels pass over rib I when passing between the axillary inlet and thorax.
Cervical components of the brachial plexus pass directly from the neck through the axillary inlets to enter the upper limb.
In the neck, the two important vertebral levels (Fig.