  We present a high spatial-resolution HST/NICMOS imaging survey in the field
of a known protocluster surrounding the powerful radio galaxy MRC1138-262 at
z=2.16. Previously, we have shown that this field exhibits a substantial
surface overdensity of red J-H galaxies. Here we focus on the stellar masses
and galaxy effective radii in an effort to compare and contrast the properties
of likely protocluster galaxies with their field counterparts and to look for
correlations between galaxy structure and (projected) distance relative to the
radio galaxy.
  We find a hint that quiescent, cluster galaxies are on average less dense
than quiescent field galaxies of similar stellar mass and redshift. In fact, we
find only two (of nine) quiescent protocluster galaxies are of simliar density
to the majority of the massive, quiescent compact galaxies (SEEDs) found in
several field surveys. Furthermore, there is some indication that the
structural Sersic n parameter is higher (n ~ 3-4) on average for cluster
galaxies compared to the field SEEDs (n ~ 1-2) This result may imply that the
accelerated galaxy evolution expected (and observed) in overdense regions also
extends to structural evolution presuming that massive galaxies began as dense
(low n) SEEDs and have already evolved to be more in line with local galaxies
of the same stellar mass.
