As part of my research, I came across references to the corpora cavernosa. These are cylindrical structures within the shaft of the penis that run down either side of the urethra (the central tube that urine and semen come down). It has also been established that the body (or shaft) of the internal clitoral organ has equivalent structures. The corpora cavernosa are mentioned in both Kinsey’s work and Hite’s. So they have been known about for some time. The corpora cavernosa trap blood and cause the penis to become erect. So it seems logical to assume that they are likely to have a similar role (even if largely defunct or less efficient) in the clitoral organ.[i]
Our instinctive sexual responses occur within the body or the brain. So it is difficult to provide hard evidence of the physiological processes involved. From observing my partners, men clearly start by getting an erection. The flaccid penis has little sensitivity. A man can enjoy having his flaccid penis stimulated gently by mouth. But the pleasure probably comes from the turn-on of having a partner interacting with his genitals. It is primarily once the penis is erect that men seem to enjoy the optimal pleasure of stimulation. Men always stimulate the penis directly in order to achieve orgasm. Intercourse, fellatio and male masturbation all stimulate the penis directly. The stimulation technique is consistent. It involves massaging the shaft of the penis (containing the corpora cavernosa) and over the glans.
When I masturbate, as I get close to orgasm, I push my fingers down into the spongey tissue either side of the labia majora. I also thrust forward with my hips and tense my buttock muscles from behind to create internal pressure. This stimulation technique didn’t make sense to me. But it always had to be the same. Later I learned that the clitoral crura (connected to the corpora cavernosa) are located either side of the labia majora. I concluded that my stimulation technique massages (as much as one can) the body of internal clitoral organ. This would mean that there were parallels between my own and the male experience of arousal and orgasm. This theory is difficult to prove categorically but it is certainly a possible explanation.
I realised that female masturbation involves emulating the male role in intercourse. The clitoris is never erect but the clitoris can be tumescent. I could see and feel my physical arousal in middle age (unconnected with any mental arousal). When masturbating, I feel mild physical excitement that I interpret as my body responding to the fantasy I am thinking about. The male response to turn-ons is rapid. A responsive woman needs to generate arousal consciously, which takes time and depends on being alone.
[i] The female clitoral system has a precisely analogous pair of bulbous corpora cavernosa, which similarly fill with blood during sexual excitation. (Shere Hite)
Excerpt from Understanding Sexual Response (ISBN 978-0956-894762)