coitus posterior.
后横位性交

normal libido, coitus, and climax
正常性欲, 性交及性欲高潮

To engage in coitus or sexual intercourse.
进行交媾过性交。

The vagina receives the penis during coitus.
阴道在性交过程中容纳阴茎。

You have it wrong. coitus means to make babies
你搞错了吧，交配是造人的意思

Their meeting is usually about as a result of coitus.
精卵相遇通常是性交得结果。

This, in turn, has increased their enjoyment of coitus.
继而，这又增添了他们性交合的乐趣。

Coitus interruptus is not a very reliable method of birth control.
体外排精避孕法不是一种可靠的节育方法。

Re aching org asm long after the beginning of coitus is a common male dysfunction.
性交长久以后才达到性高潮是男性常见的性功能障碍。

Reaching orgasm shortly after the beginning of coitus is a common female dysfunction.
性交开始不久后就达到性高潮是女性常见的性功能障碍。

This is not only ineffective, but may also interfere with coitus and cause discomfort.
这种做法不仅无效，而且也可能干扰性交和导致不适。

The most obvious and most reliable way of avoiding pregnancy is complete abstinence from coitus.
避免怀孕最显而易见和最可靠得方法是禁绝性交。

During sexual excitement, these walls secrete a watery substance which serves as a lubricant coitus.
在性兴奋期，阴道壁分泌水样液体，以备性交时润滑的需要。

a contraceptive method in which coitus is initiated but the penis is deliberately withdrawn before ejaculation.
性交中在射精前阴茎有意抽出的节育方法。

By13 days5 minutes after coitus, the head process invaginating in the primitive pit move straight forward in cephalic derection to form the notochordal cord.
交配后13时5分，原窝底部的头突向前延伸形成管索管。