Tear duct
From Memory Alpha, the free Star Trek reference
Tear ducts are found between the eyes and the nose, they serve the purpose of tear drainage and express extreme emotion in most species.
The tears of female Elasians caused men's hearts to be enslaved if they came in contact with his flesh. (TOS: "Elaan of Troyius")
Spock once claimed that Klingons lack tear ducts. (Star Trek VI: The Undiscovered Country)
