Can't find source code for building mysql

I'm trying to follow the [instructions](http://dev.mysql.com/doc/refman/5.6/en/source-installation.html) for building MySQL from source. They guide me to a [link](http://dev.mysql.com/doc/refman/5.6/en/getting-mysql.html) where I can download the latest GA. I end up at the downloads [page](http://dev.mysql.com/downloads/mysql/) , where I can download mysql-5.6.19-osx10.7-x86_64.tar.gz for my mac, and then untar and unzip. All good so far. But when I try to cmake . per the instructions, I get an error saying that it can't find CMakeLists.txt. Poking around looking for that, I've discovered that the download doesn't come with any actual source code except .h files. In fact, the download looks like an already-built setup with binaries such as mysqld already there. I am probably missing something obvious, but I can't figure out where I'm supposed to get the full source code and the makefile, if not from the links provided under the title, "Installing MySQL Using a Standard Source Distribution". Anyone have an idea?