the widest and most dilatable part of the male urethra canal which runs almost vertically through the prostate from its base to its apex, lying nearer its anterior than its posterior surface; this portion of the urethral canal is spindle-shaped, being wider in the middle than at either extremity, and narrowest below, where it joins the membranous portion; it is lined by transitional epithelium and contains in its posterior wall, or floor, the orifices of the prostatic utricle, ejaculatory ducts, and prostatic ducts, collectively known as the seminal colliculus (aka verumontanum) [ http://www.informatics.jax.org/accession/anna ]