There are two different kinds, viz. the Antagonists and the Congenerate; the former are those that produce opposite Motions; as a Flexor and an Extensor, a Depressor and a Levator. The Congenerate are those that contribute to one and the same Action; as when there are two Flexors or two Extensors, and then one supplies the defect of the other; whereas when one of the Antagonist Muscles is cut, the other becomes useless, and void of Action.
How is the Action of a Muscle perform'd?
It is done by Contraction and Extension; the former causeth the Antagonist to swell, and the other compels it to stretch forth in length.
What is Aponeurosis?
It is the continuity of the Fibres of a Tendon which makes a Connexion that serves to strengthen the Muscle in its Motion.
C H A P VII.
Of the Myology, or Anatomy of the Muscles of the Head.
How many Muscles are there appointed to move the Head, and which be they?