git support for subprojects?

Say that I have projects A and B which both depend on another project Z. 
Whenever I update one of those projects, I'd like to also update to the 
latest version of Z in a subdirectory. Is there that kind of support for 
these subprojects? If I'm not being clear, I'm talking about the kind of 
support that is available in Subversion through svn:externals or something 
analogous.

Also, please cc me in any answers since I'm not sure my subscription to 
the list went through.

Thanks,

Luke Powell
Project Engineer
BJ Services