Tendon sheath of extensor digitorum and extensor indicis

Vagina tendinum musculorum extensoris digitorum et extensoris indicis · Pochva šlach natahovače prstů a ukazováku

Joints & cartilage

Looks like

One sleeve around the tendons that straighten the fingers, in the middle compartment on the back of the wrist.

Lets these tendons glide under the wrist band.

Swelling here is common in rheumatoid arthritis; a painless swelling that moves with the tendons is often tenosynovitis or a ganglion.