A column of gray matter occupies the center portion of
the spinal cord. In cross-section, the gray matter looks somewhat like the letter "H" or
a butterfly. Each arm or extension of gray matter is referred to as a horn.
Projecting towards the back of the spinal cord are the posterior (= dorsal) horns,
and projecting towards the front are the anterior (= ventral) horns. In the thoracic
and upper lumbar regions of the cord, an additional pair of side projections
occur, which are called lateral horns.
Connecting the horns on either side of the cord is a transverse gray commissure.
In the middle of the gray commissure is the central canal, which contains cerebral
spinal fluid.
Two longitudinal grooves appear to nearly divide the spinal cord in half. The
shallower groove that partitions the back surface is called the dorsal (posterior)
median sulcus and the deeper groove that runs along the front surface is called
the ventral (anterior) fissure.
