Like James wrote, the anatomical upper arm demo is in the "Ziva Tools" Maya menu, under "Run Demo->Anatomical Arm".
Note that you can see the complete sequence of MEL commands to make the demo, by using the "See MEL source of demo->Anatomical Arm". This command displays the MEL source code in the Maya Script Editor. This way, you can see how to generate the anatomical arm demo by yourself.