Problems with script that prints content of a file from a given line number to the next line number specified

#!/bin/sh

START=$1
END=$2
FILENAME=$3

ERROR="[PINCH ERROR]"
if [ $# -lt 3 ]; then
    echo "$ERROR Need three arguments: Filename Start-line End-line"
    exit 1
fi

if [ ! -f "$FILENAME" ]; then
    echo -e "$ERROR File does not exist. \n\t$FILENAME"
    exit 1
fi

if [ "$START" -gt "$END" ]; then
    echo -e "$END $START"
    exit 1
fi

if [ "$START" -lt 0 ]; then
    echo -e "$ERROR Start line is less than 0."
    exit 1
fi

if [ "$END" -lt 0 ]; then
    echo -e "$ERROR End line is less than 0."
    exit 1
fi

NUMOFLINES=$(wc -l < "$FILENAME")

ENDDIFF=$(( NUMOFLINES - END ))

if [ "$START" -lt "$ENDDIFF" ]; then
    < "$FILENAME" head -n $END | tail -n +$START
else
    < "$FILENAME" tail -n +$START | head -n $(( END-START+1 ))
fi

exit 0 

The Problem I have is that if start is greater than end (exemple ./file 10 7) I need to print the the lines from start arg back to end arg (so basically line 10 9 8 7). Don't know how to do that :

if [ "$START" -gt "$END" ]; then
    echo -e "$END $START"
    exit 1
fi