I do not understand らさん in this sentence


Here is the sentence:

> 夫は涎らさんばかりの喜びようだ。

Her husband seems so happy he is almost drooling? That is, he is ecstatically
happy? What is this? らさん




夫は涎{た}らさんばかりの喜びようだ。  
This is an example of bending the rules for a literary aesthetic. The kanji
涎{よだれ} does not have the 垂{た}らす reading, but the meaning and unusual way the
author wanted the reader to read it are clear. This is relatively common even
without ふりがな in advanced novels. This usage let's the reader know the thing
being 垂らすed is 涎 without having to say it.

垂らす becomes 垂らさん because it is a classical Japanese form that is still in use
today. Another example is 溢{あふ}れんばかりの笑顔.

