For the ideas compare the striking passage in Timon, I. i. 64 ff.

3. ‘Decline your head.’

At IV. ii. 18 Goneril, dismissing Edmund in the presence of Oswald, says: 

                                  This trusty servant
     Shall pass between us:  ere long you are like to hear,
     If you dare venture in your own behalf,
     A mistress’s command.  Wear this; spare speech;
     Decline your head:  this kiss, if it durst speak,
     Would stretch thy spirits up into the air.

I copy Furness’s note on ‘Decline’:  ’STEEVENS thinks that Goneril bids Edmund decline his head that she might, while giving him a kiss, appear to Oswald merely to be whispering to him.  But this, WRIGHT says, is giving Goneril credit for too much delicacy, and Oswald was a “serviceable villain.”  DELIUS suggests that perhaps she wishes to put a chain around his neck.’

Surely ‘Decline your head’ is connected, not with ‘Wear this’ (whatever ‘this’ may be), but with ‘this kiss,’ etc.  Edmund is a good deal taller than Goneril, and must stoop to be kissed.

4. Self-cover’d.

At IV. ii. 59 Albany, horrified at the passions of anger, hate, and contempt expressed in his wife’s face, breaks out: 

See thyself, devil! 
Proper deformity seems not in the fiend
So horrid as in woman.

Gon. O vain fool!

Alb. Thou changed and self-cover’d thing, for shame,
Be-monster not thy feature.  Were’t my fitness
To let these hands obey my blood,
They are apt enough to dislocate and tear
Thy flesh and bones:  howe’er thou art a fiend,
A woman’s shape doth shield thee.

The passage has been much discussed, mainly because of the strange expression ‘self-cover’d,’ for which of course emendations have been proposed.  The general meaning is clear.  Albany tells his wife that she is a devil in a woman’s shape, and warns her not to cast off that shape by be-monstering her feature (appearance), since it is this shape alone that protects her from his wrath.  Almost all commentators go astray because they imagine that, in the words ’thou changed and self-cover’d thing,’ Albany is speaking to Goneril as a woman who has been changed into a fiend.  Really he is addressing her as a fiend which has changed its own shape and assumed that of a woman; and I suggest that ‘self-cover’d’ means either ‘which hast covered or concealed thyself,’ or ‘whose self is covered’ [so Craig in Arden edition], not (what of course it ought to mean) ‘which hast been covered by thyself.’

Possibly the last lines of this passage (which does not appear in the Folios) should be arranged thus: 

To let these hands obey my blood, they’re apt enough
To dislocate and tear thy flesh and bones: 
Howe’er thou art a fiend, a woman’s shape
Doth shield thee.