W*****B
发帖数: 4796 | 1 The coronal ridge is the part of the human penis thought to have evolved to
allow for semen displacement. Research has studied how much semen is
displaced by different shaped, artificial genitals.[45] This research showed
that, when combined with thrusting, the coronal ridge of the penis is able
to remove the seminal fluid of a rival male from within the female
reproductive tract. It does this by forcing the semen under the frenulum of
the coronal ridge, causing it to collect behind the coronal ridge shaft.[45]
When model penises without a coronal ridge were used, less than half the
artificial sperm was displaced, compared to penises with a coronal ridge.[45]
The presence of a coronal ridge alone, however, is not sufficient for
effective semen displacement. It must be combined with adequate thrusting to
be successful. It has been shown that the deeper the thrusting, the larger
the semen displacement. No semen displacement occurs with shallow thrusting.
[45] Some have therefore termed thrusting as a semen displacement behaviour.
[47]
The behaviours associated with semen displacement, namely thrusting (number
of thrusts and depth of thrusts), and duration of sexual intercourse,[47]
have been shown to vary according to whether a male perceives the risk of
partner infidelity to be high or not. Males and females report greater semen
displacement behaviours following allegations of infidelity. In particular,
following allegations of infidelity, males and females report deeper and
quicker thrusting during sexual intercourse.[45] | W*****B
发帖数: 4796 | 2 龟头不是完全的圆锥形，在腹侧向上折返，形成了一个向上纵向的的沟槽
：肯定不是这个原因：如果用来透气，凹槽就应该是纵向的，而不是横向的 |
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