Noun
(anatomy) Ellipsis of palmaris longus muscle. A muscle in the mammalian forearm which inserts into the palmar aponeurosis. In humans it is vestigial, and is absent in some people in one or both arms.
(anatomy) Ellipsis of palmaris longus tendon. A tendon in the mammalian forearm, between the flexor carpi radialis and the flexor carpi ulnaris tendons. In humans, it is vestigial and absent in about 1/8th of people in one or both arms; frequently repurposed for reconstructive surgery.
Source: en.wiktionary.org