MTHI - MIPS instruction reference

mthiMove to HI 
Copies $t1 into the special HI register, overwriting any prior multiply or divide result stored there.
Forms  mthi   
Operands $t1 Any general-purpose register, $0 to $31, using its numeric or named spelling, such as $8 or $t0 ($zero is $0; $ra is $31). 
 # Set the implicit HI register explicitly, then read it back. Inspect $t2: 42.
li $t0, 42
mthi $t0
mfhi $t2