282 ASTONISHMENT. CHAP. XII. They are highly characteristic of the expression of sur- prise or astonishment. Each eyebrow, when raised, be- comes also, as Duchenne remarks/ more arched than it was before. The cause of the mouth being opened when astonish- ment is felt, is a much more complex affair; and several causes apparently concur in leading to this movement. It has often been supposed ° that the sense of hearing is thus rendered more acute; but I have watched per- sons listening intently to a slight noise, the nature and source of which they knew perfectly, and they did not open their mouths. Therefore I at one time imagined that the open mouth might aid in distinguishing the direction whence a sound proceeded, by giving another channel for its entrance into the ear through the eu- stachian tube, But Dr. W. Ogle 6 has been so land as to search the best recent authorities on the functions of the eustachian tube, and he informs me that it is almost conclusively proved that it remains closed except during the act of deglutition; and that in persons in whom the tube remains abnormally open, the sense of hearing, as far as external sounds are concerned, is by no means improved; on the contrary, it is impaired by the respira- tory sounds being rendered more distinct. If a watch be placed within the mouth, biit not allowed to touch the sides, the ticking is heard much less plainly than when held outside. In persons in whom from disease or a cold the eustachian tube is permanently or tempo- rarily closed, the sense of hearing is injured; but this may * * Mecanisme cle la Physionomie,' Album, p. 6. 8 See, for instance, Dr. Piderit (' Mimik und Physiog1- nomik,' s. 88), who has a good discussion on the expression of surprise. 6 Dr. Murie has also given me information leading to the same conclusion, derived in part from comparative anatomy.