on crotchets

But I Digress:  The Exploitation of Parentheses in English Printed Verse – John Lennard (p.1)

Square brackets” are referred to by their proper name, ‘crotchets’…

[1.  since when are they called ‘crotchets’?]
[2.  what a way to start a book!]
[3.  yes, i am reading this book.]