Every joint in the body has one set of muscles which move
it one way and another set which move it the opposite way. Such
groups of muscles are called antagonists. The antagonists which
operate the base of the neck are the longus colli and scalenus
muscles, which act to raise the base of the neck, and the cervical
rhomboideus and trapezius muscles, which act to make it sink.
The
vertebrae of the lower neck and anterior thorax form a chain that
describes a "U" shape. The longus colli underslings this chain. When
the longus colli contracts (gets shorter from end to end), the base
of the neck is raised as a child is raised by four adults pulling on
the corners of a blanket in the Eskimo game of "blanket-tossing."
Since the vertebral chain is a connected whole, raising the base of
the neck is much easier and the horse can raise it farther if the
loins coil and all the muscles of the topline are in release (un-
braced or decontracted).
