any structural anomaly of either of the paired sac-like glandular structures situated posterolateral to the urinary bladder in the male and functioning as part of the reproductive system; each sac is pyramidal in shape and convoluted in appearance and at the anterior extremity becomes constricted into a narrow straight duct that joins the ipsilateral vas deferens to form the ejaculatory duct; seminal vesicles secrete seminal fluid and nourish and promote the movement of spermatozoa through the urethra