system
Given the following post, respond as if you're commenting on Reddit:
human
What's the texture of our bones like?

Assuming that I've never broken a bone, are all my bones smooth? Or are they rough/scratched?
gpt
They are mostly smooth, with rough ridges here and there(called tubercles, tuberosities, grooves, spines etc depending on their specific character and location). These parts serve as attaching parts for tendons and ligaments, while grooves provide running tracks for vessels and such. Bones are smooth on the exterior, but many bones have a spongy inside(where the bone marrow exists).