_What is _Synarthrosis_?_

_Synarthrosis_ being opposite to _Diarthrosis_, is a {15} close or compacted Articulation, dest.i.tute of any sensible Motion.

_How many sorts of _Synarthroses_, or close Articulations are there?_

There are Three. _viz._ _Sutura_, _Harmonia_, and _Gomphosis_.

A _Suture_ is that which joins together two Bones by a kind of Seam or St.i.tch, or by a Connexion of their Extremities dispos'd in form of a Saw, the Teeth whereof are reciprocally let one into another: Such are the Sutures of the Skull-Bones.

_Harmonia_ is the uniting of two Bones by a simple Line; as the Bone of the Cheek with that of the Jaw.

_Gomphosis_ is a kind of close Articulation, which unites two Bones after the manner of Nails or Wooden Pins fixt in the Holes made to receive them: Such is that of the Teeth in their Sockets.

_What is _Symphysis_?_

_Symphysis_ is the uniting of two Bones by the interposition of a _Medium_, which ties them very streight together, being also threefold: Such is the Connexion of the Knee-Pan or Whirl-Bone of the Knee, and the _Omoplata_ or Shoulder-Blade.

_Are not these three kinds of Articulations or _Symphyses_ distinguish'd one from another?_

Yes; for tho' they are all made by the means of a third Body intervening, which joins them together; nevertheless every one of these various Bodies gives a different Denomination to its respective Articulation: Thus the Articulation which is caus'd by a Glutinous and {16} Cartilaginous Substance, is properly call'd _Synchondrosis_; as that of the Nose, Chin, _Os Pubis_, _&c._ But an Articulation which is made by a Ligament is termed _Synncurosis_, as that of the Knee-Pan. Lastly, that which is wrought by the means of Flesh, bears the Name of _Syssarcosis_; as the Jaw-Bones, the _Os Hyoides_, and the _Omoplata_ or Shoulder-Blade.

_Have the Bones any sense of Feeling or Motion?_

They have neither; for their sense of Pain proceeds from nothing else but their _Periostium_, or the Membrane with which they are cover'd, and their Motion is perform'd only by the Muscles that draw them.

_Doth the Marrow afford any Nutriment to the Bones?_

No, all the Bones are nourish'd by the Blood, as the other Parts; but the Marrow is to the Bones what the Fat is to the Flesh; that is to say, it is a kind of Oil or Unctuous Substance, which moistens, and renders them less brittle.

_Are all the Bones of the same Colour?_

No, they follow the Temperament and Const.i.tution of the Persons.

_How many in number are the Bones of the Humane Skeleton?_

There are two hundred and fifty usually reckon'd, _viz._ 61 in the Head, 67 in the Trunk or Chest, 62 in the Arms and Hands, and 60 in the Legs and Feet; but the true Number cannot be exactly determin'd, by reason that some Persons have more, and others fewer; for some have more _Ossa Sesamoidea_, Teeth and {17} Breast-Bones than others: Again, some have many indentings in the _Lambdoidal_ Suture, and others have none at all.

_Can you rehea.r.s.e the Number of the Bones of the Head?_

There are Fifteen in the Skull, and Forty six in the Face.

The Fifteen of the Skull are the _Coronal_ for the fore-part of the Head; the _Occipital_ for the hinder-part; the two _Parietals_ for the upper-part and each side; the two _Temporals_ for the Temples; the _Os Sphenoides_ or _Cuneiforme_, which closeth the _Basis_ or bottom of the Skull; the _Os Ethmoides_, or _Cribriforme_, situated at the Root of the Nose; and the four little Bones of the Ear on each side, _viz._ the _Incus_ or Anvil; the _Stapes_ or Stirrup; the _Malleolus_ or Hammer; and the _Orbiculare_ or Orbicular Bone.

Of the Forty six of the Face, Twenty seven are counted in the Upper-Jaw, _viz._ the two _Zygomatick_, or the two Bones of the Cheek-Knots; the two _Lachrymal_ in the great Corners of the Eyes toward the Nose; the two _Maxillar_, that receive the Upper-Teeth, and which form part of the Palate of the Mouth, and the Orbits of the Eyes; the two Bones of the Nose; the two Palate-Bones which are at its end, and behind the Nostrils; the last being single is the _Vomer_, which makes the Division of the lower part of the Nostrils; and there are generally Sixteen Upper-Teeth. The Lower-Jaw contains Nineteen Bones, _viz._ sixteen Teeth; two Bones that receive them; and the _Os Hyoides_, which is single, and fix'd at the Root of the Tongue.

{18}

_How are the Teeth usually divided with respect to their Qualities?_

Into _Incisive_ or Cutters, _Canine_ or Dog-Teeth, and _Molar_ or Grinders: There are eight Incisive, and four Canine, which have only one single Root; as also twenty Molar, every one whereof hath one, two, or three Roots.

_Can you recite the Number of the Bones of the Trunk or Chest?_

There are generally thirty and three in the _Spine_ or Chine-Bone of the Back, _viz._ seven _Vertebra's_ in the Neck, twelve in the Back, five in the Legs, five, six, and sometimes seven in the _Os Sacrum_, three or four in the _Coccyx_, and two Cartilages at its end.

There are twenty nine in the Breast, _viz._ twenty four Ribs, two Clavicles or Channel-Bones and commonly three Bones in the _Sternum_. The Hip-Bones are likewise divided into three, _viz._ _Ilion_, _Ischion_ and _Os Pubis_.

_Do you know the Number of the Bones of the Arms?_

There are thirty and one Bones in each Arm, that is to say, the _Omoplata_ or Shoulder-Blade; the _Humerus_ or Shoulder-Bone; the two Bones of the Elbow call'd _Ulna_, and _Radius_; eight little Bones in the _Carpus_ or Wrist; five in the _Metacarpium_ or Back of the Hand; and fourteen in the Fingers, three to every one except the Thumb, which hath only two.

_Can you give us a List of the Bones of the Leg in their Order?_

There are thirty Bones in each Leg, _viz._ the _Femur_ or great Thigh-Bone, the Knee-Pan or {19} Whirl-Bone on the top of the Knee; the _Tibia_, _greater Focile_, or Shin-Bone; and the _Perone_ or _Fibula_, or _lesser Focile_, which are the two a.s.sociated Bones of the Leg; seven little Bones in the _Tarsus_; five in the _Metatarsus_; and fourteen in the Toes; that is to say, three to every one, except the great Toe, which hath only two.

Thus the Number of Bones of the Humane _Skeleton_ amounts to two hundred and Fifty, without reckoning the _Sesamoides_, the Indentings of the Skull, and some others which are not always to be found.

CHAP. VI.

_Of Myology, or the Anatomy of the Muscles of a Humane Body._

_What is a Muscle?_

It is the princ.i.p.al Organ or Instrument of Motion; or it is a Portion of Flesh, wherein there are Veins, Arteries, Nerves, and Fibres, and which is cover'd with a Membrane.

_How many parts are there in a Muscle?_

Three, _viz._ the Head, the Belly, and the Tail: The Head is that part thro' which the Nerve enters; the Belly is the Body or Middle of the Muscle; and the Tail is the Extremity, where all the Fibres of the Muscle are terminated to make the Tendon or String which is fasten'd to the Part whereto it gives Motion. {20}

_Have all the Muscles their Fibres streight from the Head to the Tail?_

No, some have them streight, others transverse, and others oblique or circular, according to the several Motions to which they are appropriated.

_How many sorts of Muscles are there with respecting to their Action?_

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.