vas deferens A spermatic duct especially of a higher vertebrate that in the human male is a thick-walled tube about two feet (0.61 meters) long that begins at and is continuous with the tail of the epididymis and eventually joins the duct of the seminal vesicle to form the ejaculatory duct. BTO:0001427 BrendaTissueOBO deferent duct ductus deferens internal male genital organ