The picture below shows a rear view of the back and buttocks of a human being.
The shape of the back and buttocks are then outlined.
The shape created by the outline is similar to the shape of a penis. It will be easier to demonstrate that similarity if the picture is first flipped vertically.
The flipped back and buttock picture is then compared to an actual penis.
The similarity between the shape of the buttocks and the head of the penis is highlighted in this picture,
while the similarity in shape between the orientation and shape of the back is highlighted in this picture.
And finally a picture outlining the entire penis and all of the back and buttocks to highlight their overall shape similarity.
