E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Liver-vein (The).
A love rhapsody. The liver was anciently supposed to be the seat of love. When Longaville reads the verses, Biron says, in an aside, This is the liver-vein, which makes flesh a deity. (Shakespeare: Loves Labours Lost, iv. 3.)