>>149873296
Just based on what we see already, there's enough to conclude that their 'blocks' fulfill the role of bones and muscles at the same time. Their outer anatomy also implies they would feel similar to the touch, but not identical (eg. if you grabbed Pearl's wrist you'd feel the cylinder shaped block underneath, not wrist bones)

>the gems have skin, saliva, and sweat, we even briefly see Garnet's blood
>all gems have fingers and toes
>some larger soldier gems have defined deltoids and biceps, which again shouldn't be needed without a muscular system, but the shape is still present
>all gems have mouthes, complete with full sets of teeth and a tongue, even though they do not eat and wouldn't need to chew (but they do need to speak)
>the features that gems are missing compared to humans (in canon) are few and far between, with the only exception being ears, which they don't have. Humans are otherwise just as low detail.

I bet gem blood has different properties too. In the show they 'poof' before you can see any come out, but based on their mineralogy, some may shoot hot wax if you cut them and it could burn you, while others may have mineral oil come out, which instead would be useful to store for later.