I am reviewing bones and their muscles, and how to use them in ballroom and Latin dancing.

Arm to hand:

Upper arm - humerus bone (one bone) with three major muscles -- biceps, deltoid and triceps. Biceps flexes the arm like a flower closing. Triceps extends the arm  like a flower opening. Deltoid moves the arm to the side like a bird's wing. 

Lower arm - radius and ulna (two bones) with two major muscles -- pronator teres and pronator quadratus. Both muscles pronate (turns the hand palm down) [Pronation means face down; supination means face up]. 

Hand -- carpels, metacarpals and phalanges (I haven't studied the hand muscles yet). The carpels are the bones in the wrist and palm. The metacarpals are the bones in the palm. The phalanges are the bones of the fingers. There are three bones in each phalanges (finger) except for the thumb which has two. 

It is interesting that muscles only work by shortening the distance between their two end attachments. They can't lengthen, though then can relax. Because of this, most muscles work in pairs. For example, the biceps work opposite of the triceps. 

Once I finish reviewing the rest of the arm and hand, I'll write about their function in dancing.