skip to content

Darwin Correspondence Project

From Hubert Airy   3 April 1871

Flamsteed House | Greenwich S.E.

1871. April 3.


I venture to take the liberty of writing to you, in the belief that even the smallest fact that bears on your grand study will be interesting to you in its degree.

I notice at p. 19 in Vol. I of your new work, that the ‘platysma myoides’ is thought not to admit of voluntary action. To this general rule I can produce an exception in my own person, for I have the power at will of throwing the whole of that skin-muscle into strong contraction, puckering the skin, somewhat like the cicatrix of a burn, with strongly-marked fan-like lines of tension stretching down below the clavicles and over the ‘pectoralis major’ towards the axillæ.1 I can do this on either side separately, or on both sides at once. The action begins in that part of the muscle which lies between the lower jaw and the angle of the lip, and extends by effort to the descending fibres. The topmost fibres (‘risorius’) aid in the ordinary act of smiling; but as the lower fibres gradually come into play, the smile gradually passes into an intense sardonic grin.

I find also that the retraction of the scalp by the occipital portions of the ‘occipito-frontalis’ is associated with a contraction of the ‘retrahens aurem’ giving a slight backward pull to the external ear.

(Pray allow the great interest I take in your researches, to be my apology for troubling you with these details.)

With regard to the loss of voluntary movement of the ears, in man and monkey, may I ask if you do not think it might have been caused, as it is certainly compensated, by the facility and quickness in turning the head, possessed by them in virtue of their more erect stature, and the freedom of the atlanto-axial articulation? (In birds the same end is gained by the length and flexibility of the neck.)

The importance, in case of danger, of bringing the eyes to help the ears, would call for a quick turn of the head whenever a new sound was heard, and so would tend to make superfluous any special means of moving the ears, except in the case of quadrupeds and the like, that have great trouble (comparatively speaking) in making a horizontal turn of the head,—can only do it by a slow bend of the whole neck.

Asking your pardon for the liberty I have taken, I remain, Sir, with great respect, Yours truly | Hubert Airy

CD annotations

2.9 The topmost … grin. 2.11] scored red crayon; ‘Expression’2 red crayon
5.2 may … neck.) 5.5] scored red crayon
6.1 The importance … neck. 6.5] ‘Hedgehogs(?) opposed (Rolleston)— Lizard opposed’3 pencil
Top of letter: ‘Keep’ pencil; ‘& Expression’ red crayon


CD removed the phrase ‘but cannot be voluntarily brought into action’ from the third printing of Descent 1: 19.
CD discussed the platysma myoides in Expression, pp. 298–303.
CD discussed voluntary muscle action in hedgehogs in Expression, pp. 101–2. CD refers to George Rolleston, and possibly to the letter from George Rolleston, 22 February 1871, although Rolleston mentioned the resemblance between human and porcupine, not hedgehog, ears. CD’s annotations are for his letter to Hubert Airy, 5 April [1871].


Comments on discussion of residual organs in Descent [ch. 1].

Describes his ability to contract the platysma myoides at will.

Suggests reason for loss of voluntary movement of ears in men and monkeys.

Letter details

Letter no.
Hubert Airy
Charles Robert Darwin
Sent from
Source of text
DAR 87: 37–8
Physical description
4pp †

Please cite as

Darwin Correspondence Project, “Letter no. 7657,” accessed on 17 July 2019,

Also published in The Correspondence of Charles Darwin, vol. 19