What is the best medium/material for printing an anatomic model for educational or study purposes? Specifically, I'm interested in printing intricate head and neck bony anatomy that requires fine detail to look at important holes and "cracks"/fissures.
The Stack Exchange discourages "best" type questions, as any answers are going to be opinion based. There are going to be more opinions than types of materials and types of printing.
Your question regarding specifics is more on the mark, however, and has less to do with material than with method.
Consider that resin based printing, especially SLA printers will provide extremely fine detail at extremely fine prices. SLA printers are more commonly used for smaller models such as jewelry and dental applications.
SLS, Selective Laser Sintering is capable of nearly as detailed work as SLA and is better suited for larger models. One can contract for SLS work on the major 3D printing services. Pricing for SLS is also "up there." Use The Google to locate 3D printer services for a suitable resource.
In the FDM world, you'll find lower costs and lower resolution. My printer is capable of 0.100 mm layer thickness, which means barely visible layer lines, but they are still quite obvious, especially on sloped or slanted surfaces.
I suggest that you find a small scale or segment of the part you wish to have printed and send it off for sample returns in the above formats.
As an option, once you have the parts, you could consider to use them to create molds and cast in resin as many copies as you would need.