"Constrain Proportions" checkbox not in Image Size dialog box!

[LosFelizGirl]

"Constrain Proportions" checkbox not showing up in Image Size dialog box.  Where did it go? 
I have an older version of Photoshop and it appears there, but not in my version 26.3

I attached both Image Size dialog boxes from each version so you can see what I am referring to.

Please advise! 

[LAMY2017 · Accepted solution]

I vaguely remember the box! Thankfully, the chain icon between Width and Height is a toggle between Constrain/No Constrain.