index finger

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The distance between the index finger and the thumb was estimated to be on average 69 per cent larger than the actual size of the participants’ hands.
关于食指与拇指之间的距离，估计值比参与者左手食指与拇指的实际距离平均要长69%。
Boys exposed to high levels tend to have a longer ring finger relative to their index finger, while in males exposed to lower levels, the two fingers tend to be a similar length.
暴露在高水平性激素环境里的男孩，其无名指相对于他们的食指更长，而低水平环境中，这两根手指趋近于等长。
In the most basic reaction-time tests, for example, the subject must react when a light goes on by lifting her index finger off a home button and immediately depressing a response button.
例如，在最基本的反应时间测试中，要求指示灯一亮，受试者的食指必须迅速离开原来所处的（键盘上的一个）键（基位键）而立即按下（按照指示灯要求作出回应的那个）回应键。

And another British study reported last year that people whose index finger is shorter than their ring finger are at higher risk of osteoarthritis.
The longer the ring finger and the shorter the index finger, the greater the testosterone exposure.
A way to know how much is to compare their ring finger to their index finger.

Indians pitcher Ray Lamb sprains his right index finger and doesn't play again until June 28.
NPR: Players Hurt In Basebrawls