Figure 1.

Shape correspondence of male and female genitalia. The silicone vaginal endocast is lined up with the inflated penis tip in sexually mature (a) harbour porpoises (Phocoena phocoena), (b) common bottlenose dolphins (Tursiops truncatus), (c) short-beaked common dolphins (Delphinus delphis) and (d) harbour seals (Phoca vitulina). Male and female genital are aligned in the positioning and angle that would enable the deepest penile penetration. Anatomical landmarks identified on the vaginal endocast include the (1) proximate cervix, (2) vaginal folds and (3) vaginal opening. Anatomical landmarks identified on the penis include the (4) penis tip or glans to sheath, (5) penis shaft and (6) penis retractor muscle.