We name the Arm Lines for
how they are arranged in the armpit
(Image 3). The pectoralis major is
part of the Superficial Front Arm Line
(SFAL) (Image 4A). The pectoralis
minor and subclavius, and the fascia
that surrounds them, are part of the
Deep Front Arm Line (DFAL). In the
back, the trapezius and deltoid form the
beginning of the Superficial Back Arm
Line (SBAL) (Image 4B). Beneath these
are the rhomboids and levator scapulae
leading to the rotator cuff of the Deep
Back Arm Line (DBAL). These lines
terminate in the four corners of the
hand—the palm, thumb, back of the
hand, and little finger respectively.
Because the intricate anatomy is
beyond the scope of a short article, you
can follow the individual structures
in each line by following the charts
in Image 4. For simplicity, you can
best visualize the four Arm Lines
as the four aspects of a bird’s wing.
Lean forward and stick your arms
out like a kid playing airplane: the
SFAL is the bottom of your wing
from pectorals to palm; the SBAL is
the top of your wing from trapezius