synovial sheath of 5th finger continuous with common flexor sheath

synovial sheath of thumb continuous with radial bursa - synovial sheath of flexor pollicis longus

basically continuous with tendons that run in carpal tunnel

https://www.nysora.com/topics/regional-anesthesia-for-specific-surgical-procedures/upper-extremity-regional-anesthesia-for-specific-surgical-procedures/anesthesia-and-analgesia-for-hand-procedures/digital-block/

#anatomy-hand