Difference between signal related structures

[Pranav Sawargaonkar]

Hi
I am studying signaling related work in FreeBSD kernel just for learning.
Can anybody tell me that why there are two different structures named
1)struct   sigcontext
2)struct   osigcontext
are defined in /sys/i386/include/signal.h
I want to know what is basic difference between them?
Thanks in advance

                                           -Pranav  Sawargaonkar