J.R. Bray may be remembered for running the first successful American animation studio, but movie cartoons made up only a part of the output. He produced and distributed a large number of documentaries, including this one, about how the human body, from the sinuses down through the epiglottis, produce sound. To bring the matter full circle, the shots showing the open mouth and the spaces and organs are all animated. After all, he had the staff.
It's competently done, with the various bodies clearly marked off and labelled, even if the style of drawing is rather simple and plain. There's nothing odd about that. When you wish to show the interior where the sound is produced, there's little sense in elaborating on the outside. Especially when it's expensive.