The third is the Masseter, which hath two
Sources or Beginnings, and as many Insertions; the first Source thereof is at the Cheek-Knot or Ball of the Cheek, and the second at the lower part of the Zygoma. The first Insertion is at the outer Corner of the Jaw, and the second in the middle part, by that means forming the Figure of the Letter X.
The fourth is the Pterygoideus or Aliformis Internus, which hath its beginning in the Apophysis Pterygoides, and is terminated in the inner Corner of the Jaw; so that Mastication or Chewing is perform'd by the means of these four Muscles.
How many Muscles are there in the Face, and which be they?
There are two for the Forehead, call'd Frontal, whose Origine is in the upper part of the Head, from whence they descend by streight Fibres, until they are fasten'd in the Skin of the Forehead near the Eye-Brows, where they are re-united: Their Action or Office is to draw the Skin of the Forehead upward, whereto they stick very close.
There are also two others call'd Occipital, which have their Beginning in the same place with the preceeding, but they descend backward, and cleave to the Skin of the hinder part of the Head, which they draw upward.
There are two Muscles to each Eye-Lid, one whereof is termed the Attollens or Elevator and the other the Depressor. The Elevator takes its rise in the bottom of the Orbit of the Eye, and is fastned by a large Aponeurosis to the edge of the upper Eye-Lid. The Shutter or Depressor, call'd also the Orbicular, hath its Origine in the great Canthus, or Corner of the Eye, passeth over the
Eye-Lid upward, and is join'd to the lesser Corner of the same Eye, being extended along its whole Compass.
The Eyes have each six Muscles, viz. four Recti and two Obliqui; the Recti or streight Muscles are the Elevator, the Depressor, the Adductor, and the Abductor. The first of these call'd Elevator, or Superbus, draws the Eye upward, as it is pull'd downward by the Depressor or Humilis; the Adductor or Bibitorius draws it toward the Nose, and the Abductor or Indignarorius toward the Shoulder: All these small Muscles have their Originals and Insertions in the bottom of the Orbit through which the Optick Nerve passeth, and are terminated in the Corneous Tunicle, by a very large Tendon.
The first of the Oblique ones is term'd the Obliquus Major, and the other Obliquus Minor, because they draw the Eye obliquely. These Muscles cause Children to squint when they do not act together. The Obliquus Minor is fasten'd at the outward part of the Orbit near the great Corner, and draws the Eye obliquely toward the Nose: But the Obliquus Major is fixt in the inner part of the Orbit, and ascends along the Bone to the upper part of the great Corner, where its Tendon passeth thro' a small Cartilage nam'd Trochlea, and is inserted in the little Corner with the lesser Obliquus Minor, to draw the Eye obliquely toward the lesser Corner.