The anatomy of humane bodies epitomized wherein all parts of man's body, with their actions and uses, are succinctly described, according to the newest doctrine of the most accurate and learned modern anatomists / by a Fellow of the College of Physicians, London.

CHAP. VII.

Of the Muscles of the lower Jaw.

THE lower Jaw (for the upper is immoveable, and therefore has no Muscles) is moved up∣wards, downwards, towards the right side, to∣wards the left side, and towards the back-part. To procure these motions five pair of Muscles are appointed,* 1.1 of which there is only one pair that draweth the Jaw downwards, all the others in some measures upwards: whence one may be easily made to shut his Mouth, there being only one pair of Muscles to oppose; but it is difficult to open it against ones will, through the great strength of the Muscles that shut it.

The first pair of Muscles is called temporale,* 1.2 and is the strongest and largest: It springeth from the bones of the frons, synciput, temples and sphenoides, with a fleshy, large and semicircular beginning, and on its outer side is covered with the pericrani∣um, its inner lying next the periosteum. Its Fibres the further they are from its middle, the more obliquely are they carried towards its Tendon, for the further it descends, the narrower (but thicker and more carnous) it grows; and at length passing under the os jugale, it embraceth and is inserted into the acute process of the lower Jaw (called 〈 in non-Latin alphabet 〉〈 in non-Latin alphabet 〉) with a short but very strong Tendon. Spigelius says, this Tendon is extended through the whole Muscle, in its middle fleshy substance. Wherefore if this Muscle be wounded,

fearful symptoms ensue,* 1.3 partly because the Ten∣don passeth so; partly because it is covered with the pericranium. This Muscle forcibly pulleth up the lower Jaw, and so shutteth the Mouth. The Second pair is called deprimens, digastricum, or bi∣ventre, because it hath two bellies,* 1.4 between which a Tendon lyeth: this doth pull down the Jaw, and so openeth the Mouth. Wherein it is partly assisted by the Quadratus described in the forego∣ing Chapter. It hath its beginning from the pro∣cess of the bone of the Temple, called Styloides, where it is nervous and broad; and afterward becoming fleshy, small, and round, it passeth downward, and in its middle, where it comes to the flexure of the lower jaw-bone, it loseth its fleshy substance, and degenerates into a nervous and round Tendon; but by and by it becomes car∣nous again, and goes along the inner side of the lower-jaw, to its forepart that is under the Chin, where it is inserted.* 1.5 The third is called masseter, because it serveth for chewing by moving the Jaw to the right and the left side: from its situation it may be called laterale. This hath two beginnings: one is nervous, springing from the suture where the first bone of the Jaw is joyned to the fourth. This beginning is large and strong. The other beginning is fleshy, proceeding from the os jugale, and so marcheth towards the Chin, and is implan∣ted into the whole breadth of the lower Jaw strongly. The Fibres of this Muscle, by reason of the two beginnings, cross one another; so that these Muscles do not only move the Jaw laterally,* 1.6 but backward and forwards also.

The fourth pair is called pterygoideum externum, aliforme externum, or maxillam abducens. This hath

also a double beginning, partly nervous and partly fleshy; springing partly from the upper external sides of the wing-like process of the os sphenoides, partly srom the rough and sharp line of the same bone. Whence marching down by streight Fibres, it becometh greater and thicker. And at length is inserted by a strong Tendon into the internal lateral part of the lower Jaw, which is under the Tendon of the temporal Muscle. This moveth the Jaw forward, which appeareth when the lower Teeth are stretched further out than the upper.

The fifth pair is termed maxillam adducens, or pterygoideum internum.* 1.7 This draweth the Jaw to∣wards its head, or backward. This, in the be∣ginning being nervous, doth spring from the inner cavity of the wing-like Process of the os sphenoides; then becoming fleshy, large and thick, and marching down by a streight passage, it is inser∣ted into the inner and hinder part of the lower Jaw by a nervous, broad and strong Tendon. Besides its more proper Action of drawing the Jaw backwards, it also helps the temporal Muscle to draw it up.

Notes

• * 1.1

  The lower jaw hath five pair of muscles.
• * 1.2

  1. Tempo∣rale.
• * 1.3

  Why the wounds of the tempo∣ral muscle are dange∣rous.
• * 1.4

  2. Deprimens or biven∣tre.
• * 1.5

  3. Masseter or laterale.
• * 1.6

  4. Aliforme exter∣num, or maxillam abducens.
• * 1.7

  5. Alitorme internum, or maxil∣lam addu∣cens.