This image is DJ and Nikka from Michael Rosen's book Vanilla Sex.  You can get a free download of the entire PDF book at www.michaelrosen.com. Select "Vanilla Sex" under GALLERIES in the left column, then click on "downloadable PDF" on the Vanilla Sex page, and then click "Download" on the download page if you agree to the licensing terms. - Image by Michael Rosen
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Erectile Tissue

Vascular tissue capable of filling with blood and becoming rigid. The tissue in the penis that becomes erect during arousal.