In some of my presentations I discuss the role of institutions in our ancestor's lives. Our ancestors were institutionalized in insane asylums, hospitals, sanitarium, facilities (whatever term was being used) for a variety of reasons. Women could be institutionalized at their husband's whim. Children with mental disabilities were institutionalized. The elderly were institutionalized when their families could no longer care for them.
What happened when those that were institutionalized died? In some cases, family members claimed them and had them buried elsewhere. Two of my ancestors were institutionalized at an advanced age and once they passed, family members made arrangements for them to be buried in city cemeteries. But this did not always occur, maybe because of a lack of money, shame or even when there was no family left or they couldn't be found, those that were institutionalized were buried on the grounds of the institution. No headstone with their names and dates were placed on their graves. Just a very small marker with a number documented their final resting place.
(There are even some places, I know of one I'm sure there are others, where if the deceased was not claimed by family, their bodies were donated to science and later cremated).
I remember my cousin who went on a search for her grandmother's resting place. The mental health facility were she had passed told my cousin that there was no cemetery on the grounds. It was only when she went outside and started looking around that she found a janitor who admitted to where the long neglected cemetery was located on the grounds.
There are people trying to do something about these long forgotten people whose graves are often either not marked or marked with a number and no name. This link, http://today.msnbc.msn.com/id/26184891/vp/31184847#31184847 is a touching story of one man's mission to give a field of numbers their rightful names.