The sleeves are 3/4 length to close the hand up to mid forearm. For those who were not taught anatomy, the forearm refers to the part of the hand that is located between the elbow and wrist. This length of sleeve designers specially designed in order to be able to hide the fullness of hands, leaving visible only a delicate brushes.
The style of clothing, "the bat" appeared in European fashion in the 40-ies, but the real boom came in the mid 80-ies of the last century. The name of the style was due to the cut of the sleeves, resembling the flapping wings of a bat. The similarity manifests itself in the movement of hands. It is believed that designers on this finding prompted the traditional Japanese kimono.
Beautiful and comfortable model "bat" is quite relevant today, judging from the collections of leading designers in the world. And it's not an accident or a whim of fashion, the style hides some figure flaws and successfully emphasises dignity.