[Erectile mechanism studied using penile vascular casts in the dog].

The possible mechanism of penile erection was discussed based on the findings obtained by the scanning electron microscope observations of the penile vascular casts in the dog. Polsters protruding into the lumen of the distal helicine arteries regulate blood flow into the cavernous spaces. The drainage veins from the corpus cavernosum penis arose on the dorsal surface and crept on the corpus until changing direction perpendicularly. This suggested that these veins were efficiently compressed between the tunica albuginea and the corpus cavernosum penis during erection. For a high pressure to be maintained in the cavernous spaces during erection, a closed system separated from the systemic circulation must be required.