Diagrams from A System of Elocution, with Special Reference to Gesture, to the Treatment of Stammering, and Defective Articulation (1846) by Andrew Comstock. From the chapter entitled "The Postures of the Mouth":

An accurate knowledge of the positions which the organs of articulation should assume in the formation of the several elements of vocal language, is very important to those who would speak with ease and elegance. To aid the reader still further in the acquisition of this knowledge, he is furnished with the various postures of the mouth, required in uttering the elements energetically, and singly.

Comstock was hugely influential in the burgeoning science of elocution in mid-nineteenth-century America. A physician and professor of elocution at the Vocal and Polyglot Gymnasium in Philadelphia, he invented his own phonetic alphabet to improve the speech of his pupils, an alphabet which was also used to transcribe documents, including the New Testament.