The deep dorsal vein of the penis drains oxygen-depleted blood away from the glans, which is the external head of the sexual organ.
This vein runs the length of the shaft and it eventually flows into the prostatic venous plexus near a man's prostate gland. From there, the deoxygenated blood must travel through the venal system until it arrives at the center of the circulatory system for resupply with oxygen in the lungs and recirculation through the left side of the heart.
The vein is not the same as a similarly named artery, which transmits oxygenated blood to the glans. However, the deep dorsal vein of the penis runs a course close to its arterial counterpart.
It also runs directly beneath the superficial dorsal vein of the penis. However, a layer of deep fascia (connective tissue) separates the two venal blood vessels.
Since the penis is unique to male anatomy, both veins are also unique to the male body. For comparative purposes, the closest relation in the female body would include the veins servicing the clitoris.