The top of their right hand ?

Hi~, in the following sentences, what part does the pharse "the top of their right hand" mean?

Is it sams as "the back of their hand"?

Thanks~

She has each student place the top of their right hand directly under their chin. She
informs them that every time they say a syllable their mouths have to
open and close. Therefore, each time their hand moves they have said a syllable.