first evaluate $ImportFormats to see what 3D formats your platform supports.

you can then google rendering modeling raytracing search hits (there are medical models, there are realistic looking models for media making that are hollow on the inside). you may need to avoid composite models - mathematica may need a complete model rather than a file which is composed of many separate models: this would depend on the format.

i suggest that modeling a head in 3D will not "help you understand head movement"

also: mathematica does NOT specialize in optimizing live animation of large complex models like some "modelers" do, so do not expect bleeding edge speed