Lateral to the abductor hallucis is the flexor hallucis brevis, which originates from the medial cuneiform bone and from the tendon of the tibialis posterior.
Note that "brevis" is usually included to differentiate it from a "longus" muscle of the same name.
The possibility of brevis in longo is found universally across all meters, while the anceps is found only in particular verse forms.
Where it lies upon the abductor pollicis longus and the extensor pollicis brevis, it is accompanied by the dorsal interosseous nerve.
The human thumb also has other muscles in the thenar group (opponens and abductor brevis muscle), moving the thumb in opposition, making grasping possible.
The lateral surface is marked by a flat groove for the tendons of the abductor pollicis longus and extensor pollicis brevis.
The plantar surface of the base is grooved for the tendon of the abductor digiti quinti, and gives origin to the flexor digiti minimi brevis.
Being a missa brevis, several clauses of the text are set simultaneously in different voices.
