Sorry this comes so late.
This anatomy lesson is brought to you by everyone’s favourite intense af boyfriend:
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These veins are the geminated Vena epigastrica inferior aka inferior epigastric veins, which drain blood from the superficial parts of the lower abdominal wall/muscles into the external iliac vein and thus back into the main circulatory system. The less the subcutaneous or overall body fat percentage, the more they stand out under the skin. all superficial veins, they feel somewhat firm elastic, but far more easily pressed together than arteries which have much more and tighter wound muscle fibres within their walls.
Contrary to popular belief, these veins are not anatomically connected to the penile or scrotal venous system, as these veins run deeply within the groin and aren’t visible from the outside.