MUSCLES-DEEP POSTERIOR COMPARTMENT OF FOREARM, PART 2

SUMMARY

3. ABDUCTOR POLLICIS LONGUS - arises from the oblique area of radius, ulna & interosseous membrane. Inserts into the trapezium (deep part) & first MC base. Abducts thumb & wrist. Produces 'trick' flexion.    

4. EXTENSOR POLLICIS LONGUS - arises from the ulna distal to APL. Its tendon forms the ulnar boundary of the snuffbox and inserts into base of distal phalanx of thumb. Extends the terminal phalanx of the thumb.  

5. EXTENSOR POLLICIS BREVIS - arises below the APL on the radius & interosseous membrane. Its tendon lies with the tendon of the APL at the radial border of the snuffbox and inserts into the base of the proximal phalanx of the thumb. Extends the CMC & MCPJ of thumb. 
6. EXTENSOR INDICIS - small muscle that arises from the ulna distal to the EPL. The tendon joins the dorsal expansion of the index finger. Extends the index finger.

All deep extensors (other than ANCONEUS) are supplied by the PIN.

Reference(s)

R.M.H McMinn (1998). Last’s anatomy: regional and applied. Edinburgh: Churchill Livingstone.
Gray, H., Carter, H.V. and Davidson, G. (2017). Gray’s anatomy. London: Arcturus.