Question

I assure you that his lower jaw is shorter than the upper(split)​

Answer 1

Answer:

Function. The future perfect tense refers to a completed action in the future. When we use this tense we are projecting ourselves forward into the future and looking back at an action that will be completed some time later than now. It is most often used with a time expression.

Answer 2

Answer:

I assure you that his lower jaw is shorter. I assure you that his upper jaw is larger.