This is a play on words. The word "humerus" is the name of a bone which may have been broken when the Senator slipped on the banana peel. But "humerus" also sounds like "humorous" meaning inspiring that the Senator slipping caused onlookers to laugh.
Arriving late , Senator Kennedy slipped on a banana peel and fell in a heap , resulting in a humerus break in the midst of the subcommittee ' s intense discussion .