The spine is composed of a number of different curves
E, cervical, at upper portion of neck.
K, dorsal, middle of back.
L, lumbar, lower part of back, which falls behind umbilicus (position H). X '
M, sacrum, receding into a hollow between the gluteus muscles (Fig. 3, S).
N, coccyx, extreme end of spine, curving into the body.
It is in the lumbar and cervical curves that the back takes on movement, the dorsal region remaining stationary (see Figs. 4 and 5).
On Fig. 2 dotted lines R and 0 show slope of lower part of front and back outline of trunk.
0 line starts from umbilicus H, following along rectus abdominis into middle of body (between legs).
R runs parallel from most projecting point of pelvis bone to lower part of gluteus maximus.
Note that the pelvis bone also rests in the same plane (see line P), the upper portion being tilted both forward
F: Deltoid, the manner of its insertion shown on