The lumbricals are four thin muscles (the name means worm-like) which are each associated with a finger.
The lumbricals arise from the sides of the tendons of the flexor digitorum profundus.
The 2 medial lumbricals are bipennate and are innervated by the deep branch of the ulnar nerve
The 2 lateral lumbricals are unipennate and are innervated by digital branches of the median nerve
Use the mnemonic MEAT LOAF for remembering innervation of the intrinsic hand muscles. Meat = Median nerve innervates the LOAF muscles: Lateral 2 lumbricals, opponens pollicis, abductor pollicis brevis, flexor pollicis brevis. The rest of the intrinsic hand muscles are innervated by the ulnar nerve.
The lumbricals are interesting because they form a link between the flexor tendons and the extensor tendons through their origin on the flexor digitorum profundus and their insertion onto the extensor expansion arising from the extensor digitorum tendon.
This unique anatomy enables the two main functions: