Where are the pthread functions??

When I use some of the pthread functions: pthread_join, pthread_exit they work perfect. But when I look in the pthread.h file I can't seem to find any implementations of the functions...where are they hiding??

the functions are never in any of the header files. no sense in including code in the include files!
all functions are in the libraries and i doubt if you will get source for any OS except those that are open source.

ok but I guess the functions has to be writtin somewhere. Its pretty wierd to be using functions without knowing how they look.