fall to pieces/ large joints

[vil]

Dear teachers,

Would you be kind enough to give me your considered opinion concerning the interpretation of the expressions in bold in the following sentence?

With drooping heads and tremulous tails, they mashed their way through the thick mud, floundering and stumbling between whiles, as if they were falling to pieces at the larger joints.

fall to pieces = crumble = to break into small fragments or particles

large joint = shin

V .

[dajowe]

Your joints are where your bones stick together.

Your larger joints would be your knees, elbows, hips and shoulders. Smaller ones would be in your fingers and toes, for example.

[vil]

….but because the hill, and the harness, and the mud, and the mail, were all so heavy, that the horses had three times already come to a stop, besides once drawing the coach across the road, with the mutinous intent of taking it back to Blackheath. Reins and whip and coachman and guard, however, in combination, had read that article of war which forbade a purpose otherwise strongly in favour of the argument, that some brute animals are endued with Reason; and the team had capitulated and returned to their duty.
With drooping heads and tremulous tails, they (the horses) mashed their way through the thick mud, floundering and stumbling between whiles, as if they were falling to pieces at the larger joints. (Ch. Dickens, "A Tale of Two Cities)

http://www.answers.com/topic/equine-forelimb-anatomy

V.