For bones of the skull including special features:
www.gwc.maricopa.edu/class/bio201/skull/skulltt.htm
For help in definitions and more
importantly help in pronunciation of words. In the top box, enter the word
you'd like to hear (and/or find the definition of), and click Go. On the
definition page you get, click on the 
icon, and you'll get a pop-up window. A person's voice (not a computer-generated
one) says the word. There's another one of the
icons in that box, and you can click it repeatedly to hear it again. (If you are
without sound card or speakers, I'm sorry.)
http://merriamwebster.com/.
For additional practice tests, labeling models, flash cards:
www.lagcc.cuny.edu/aplab/vdo.htm