The venomous primate that licks a brachial-gland secretion to make its toxic bite is the slow loris.
Slow lorises are nocturnal Southeast Asian primates in the genus Nycticebus. They produce a secretion from a scent gland on the upper arm, near the armpit. By licking the gland and mixing the secretion with saliva, a loris activates a defensive chemical mixture that can be delivered through a bite.
This is an exceptional trait: a toxic bite is rare among mammals and unique among primates. Slow lorises may use the toxin against predators, parasites, and other lorises during territorial or social conflicts. Females have also been observed transferring the secretion to their young during grooming, potentially protecting them while they are left hidden on branches.
The “venom” story has a scientific caveat. In captive animals, the brachial secretion resembles a major cat allergen, so some reactions may involve allergy rather than a conventional venom. Another common mistake is treating “slow loris” as one species: the name covers several Nycticebus species, including the Bengal, Sunda, Javan, and pygmy slow lorises.