A further investigation of nroff in the "man man" page presents me with
the following:
The /usr/catman directories have all been processed by nroff(1). AT&T
does not allow Silicon Graphics, Inc. to ship the nroff(1) sources for
manual pages.
To format locally added, unformatted manual pages, man requires nroff(1),
tbl(1), and neqn(1) which are contained in the Documentor's Work Bench
software option. Manual pages may be pre-formatted on systems which have
nroff, et al, and the resulting formatted versions may be installed on
IRISes which do not have the Documentor's Work Bench.
Get and install the groff package from the FSF. You can get it at
prep.ai.mit.edu:/pub/gnu (and many other places).
Richard Coleman
coleman(_at_)math(_dot_)gatech(_dot_)edu