King Lear : Act 1, Scene 5

           Enter LEAR, KENT [disguised as Caius],
           and Fool.

before ahead of me | to GloucesterThis is confusing! | these letters i.e., this letter | her demand out of the letter her questions arising from reading the letter
  1   Go you before to Gloucester with these letters.
  2   Acquaint my daughter no further with any thing
  3   you know than comes from her demand out of
  4   the letter. If your diligence be not speedy, I shall
  5   be there afore you.

  6   I will not sleep, my lord, till I have delivered
  7   your letter.


  8   If a man's brains were in's heels, were't not in
kibes chilblains, inflammation of the extremities resulting from exposure
  9   danger of kibes?

 10   Ay, boy.

thy wit shall ne'er go slip-shod i.e. your wits won't wear slippers to protect against chilblains, because your wits aren't in your heels  —The Fool probably means that King Lear's journey to Regan is just stupid.
 11   Then, I prithee, be merry; thy wit shall ne'er go
 12   slip-shod.

 13   Ha, ha, ha!

kindly 1) according to her nature; 2) with natural affection | this i.e., Goneril | crab crabapple
 14   Shalt see thy other daughter will use thee kindly;
 15   for though she's as like this as a crab's like an
 16   apple, yet I can tell what I can tell.

 17   Why, what canst thou tell, my boy?

 18   She will taste as like this as a crab does to a
 19   crab. Thou canst tell why one's nose stands i'
on's of his
 20   the middle on's face?

 21   No.

of on | that so that
 22   Why, to keep one's eyes of either side's nose; that
 23   what a man cannot smell out, he may spy into.

her Goneril? Cordelia?
 24   I did her wrong.

 25   Canst tell how an oyster makes his shell?

 26   No.

 27   Nor I neither; but I can tell why a snail has a
 28   house.

 29   Why?

 30   Why, to put his head in; not to give it away to his
 31   daughters, and leave his horns without a case.

forget my nature lose my fatherly feelings [?]
 32   I will forget my nature. So kind a father! Be my
 33   horses ready?

asses i.e, Lear's followers
 34   Thy asses are gone about 'em. The reason why
seven stars Pleiades
 35   the seven stars are no more than seven is a pretty
 36   reason.

 37   Because they are not eight?

 38   Yes, indeed: thou wouldst make a good Fool.

To take 't again perforce! to take it back again by force! —King Lear may be thinking of the fact that Goneril deprived him of fifty of his knights, and fantasizing that with those knights he could take back his kingdom by force.
 39   To take 't again perforce! Monster ingratitude!

 40   If thou wert my fool, nuncle, I'ld have thee beaten
 41   for being old before thy time.

 42   How's that?

 43   Thou shouldst not have been old till thou hadst
 44   been wise.

 45   O, let me not be mad, not mad, sweet heaven
temper mental balance
 46   Keep me in temper: I would not be mad!

           [Enter Gentleman.]

 47   How now! are the horses ready?

 48   Ready, my lord.

 49   Come, boy.

           [Exeunt Lear and Gentleman.]

maid virgin | She ... shorter Maybe this is a warning that the scene is no laughing matter. Maybe this is a dirty joke. Maybe this was not written by Shakespeare. Here's a link to various comments in the New Variorum Edition of Shakespeare.
 50   She that's a maid now, and laughs at my departure,
 51   Shall not be a maid long, unless things be cut