I have drawn this diagram to help with our discussion in this thread, but I have left out the gunungan and buntut mimi part. 
 
I think originally the top and bottom ri pandan have the same shape (hence the similar name) - hooked thorn; with the top one facing up, the bottom one facing down. In time, the bottom one gets modified with a notch on top of it. 
 
Please correct me if there are any mistakes/disagreements. I could miss some things discussed above as I browsed through it rather quickly.
		 
		
		
		
			
		
		
		
		
		
		
		
	 |