From John Wood   6 April 1871

Dear Sir

You will, I am sure, excuse the liberty I take in pointing out in your last very valuable work “On the descent of Man” a slight inaccuracy.

At p. 19 it runs.—“The platysma myoides which is well developed in the neck (of man) belongs to this system, but cannot voluntarily be brought into action”.¹ Now, like its congener, the “occipito-frontalis” this human muscle can usually be voluntarily brought into action, and in some individuals and families remarkably so.

In the lower orders of the Irish and especially in women of that class whose necks are less bound & covered up than in men, the muscle can be seen in bawling & angry gesticulation to raise folds of skin in the neck eminently expressive of disgust & contempt.² A portion of it passing over the jaw to the angle of the mouth is called the “risorius Santorini” from being first described by that famous old anatomist³

It gives rise to the “risus sardonicus” or laughing “at the wrong side of the mouth” as the saying goes,—causing a “ricanante”⁴ & lugubrious expression to the mouth, spasmodically affected in tetanus & hydrophobia & which is also to be found remarkably characteristic in horses & dogs.

I have found both largely developed in the bodies of Negroes & low caste Lascars whom I have dissected, & in one Chinaman. Both are supplied liberally by the great nerve of expression to the cutaneous muscles of the face,—“the portio dura”⁵

I have also found them well developed in monkeys, the Orang & the Chimpanzee

I have more readily taken upon myself to set right this little mistake in that you have done me the honor to speak favorably, in your book in question, of my researches upon “muscular variations in the human subject.⁶ And I beg to forward you, with this, a copy of my last paper in the “Philosophical Transactions, in which I have marked several passages bearing in an important manner upon your renowned philosophical views as to the derivation of man.⁷

The two more remarkable developements I wish to call your attention to are those described at pp 92. 93. 94 84. 85 & 80; 103 & 108. viz the occipito scapular;—the scapulo-clavicular & the supra costal which I was the first to describe in the Human Subject⁸

The second named has been since found also by D^r. Pye Smith of Guys hospital; and the last by my friend professor Turner, with whose views of the homology of the “sternalis brutorum” mentioned in your book I quite agree⁹

In my M.S. yet unpublished I have many notes of specimens which tend very much to bear out your views in the same direction and which I hope, when leisure permits from my surgical avocations, to expound at the Royal Society.¹⁰

I remain Dear Sir | Yours most truly | John Wood

Cha^s. Darwin Esqre FRS.

Down. Beckenham | Kent