  VLBA and Global VLBI observations of M87 at 43 GHz, some new and some
previously published, are used to study the structural evolution of the jet
with a spatial resolution of under 100 Schwarzschild radii. The images, taken
between 1999 and 2004, have an angular resolution of 0.00043" x 0.00021". An
edge-brightened jet structure and an indication of a large opening angle at the
jet base are seen in all five epochs. In addition, a probable counter-jet is
seen in the latter three epochs. A 22 GHz VLBA image also confirms many of the
structures seen at the higher frequency, including the counter-jet. A
comparison of the counter-jet flux density at 22 and 43 GHz reveals that it is
not free-free absorbed at these frequencies.
  Attempts to obtain speeds from the proper motions of jet and counter-jet
components indicate that these observations are undersampled. The closest pair
of images gives apparent speeds of 0.25 to 0.40c for the jet and 0.17c for the
counter-jet. These speeds should be treated as lower limits because of possible
errors in associating components between epochs. If they are real, they
indicate that the jet is oriented 30-45 degrees from the line-of-sight and that
the component speeds along the jet are 0.3-0.5c. Using the jet orientation
derived from proper motions, the spectral index of the the counter-jet, and a
jet-to-counter-jet brightness ratio of 14.4, the inferred bulk flow is
0.6-0.7c, which, given the considerable uncertainties in how to measure the
brightness ratio, is not significantly larger than the component speed.
