This painting was commissioned by Philip IV of Spain, and consists of: The princess; two meninas, or ladies-in-waiting; court dwarves Maria Barbola and Nicholas Pertusato; the princess’s chaperone; an unidentified bodyguard; Don Jose Nieto Velazquez, the Queen’s chamberlain and head of the royal tapestry works; and the artist, Diego Velazquez.
The artist is the first person from the left, looking directly at the viewer.
The King and Queen are depicted as reflections in the mirror in the background, putting them in the position of the viewer.
At that time, dwarves were denigrated for their physical deformities and of little social status. Perhaps this is reflected by Velazquez merely painting an interaction of one of the dwarfs with the Mastiff, an animal.
What Great Paintings Say, Volume 2 by Rose-Marie Hagen and Rainer Hagen, pg 263-268.