SECT. VII.
Of the Bones, Muscles, Ligaments, Tendons, and their Connections.
The bones may be considered as the timber-work of the human frame; by which this wonderful fabric is supported, and kept in its due form, that the whole may be brought into its various movements, without confusion or obstruction to each other.
The bones are the most solid parts of the human body, composed of hard and indurated fibres, striated over each other, in a manner peculiar to that substance. The bony fibres are in themselves insensible, yet as the parts are variously distributed with arteries and veins, and that the nerves must necessarily have a share in their formation, they have a peculiar sensibility, which is perceptible in some parts more than others; they cannot strictly speaking, be deemed quite insensible.
The whole bony frame is covered with a tendinous and nervous tegument, called periosteum; except such parts of the teeth as are designed for mastication, which are provided with a peculiar enamel, that is harder than the rest of the bony substance.
The periosteum is exquisitely sensible, and is the safe-guard to the substance of the bone, which is delicately tender notwithstanding it is not so sensible as the skin that covers it; insomuch that it will become carious on the least exposure to the air, or the attack of any foreign body of matter whatever; whence in wounds and fractures in general, great attention should be paid to the substance of the bone, being very subject to become carious and to exfoliation, which is of the greatest consequence; but of this I shall say more in another place.
The marrow is principally designed for the nourishment of the bones; which is evident from its being plentiest in young people, when the bones are strongest; and that when it is deficient, they become brittle, and lose their tenacity.
The marrow is contained in a cellular substance, partly in vesicles of a nervous texture, and partly bony cells. At the ends of the long bones the texture is more spungy than in the middle, where the cavity is less, but the substance is most compact. Though anatomically there is no perceptible circulation in the bones, yet, that a circulation is actually existing, is evident, from a liquor oozing out from the ends of a fractured bone in the living animal; by which a fractured bone again unites, and this is called the callus; and whilst in its liquid state, resembles the white of an egg, which gradually ossifies, and becomes as hard as the main substance of the bone.
The number of bones differ somewhat in various subjects; ordinarily they amount to two hundred and fifty-two: In the head sixty-three; in the trunk seventy; in the arms and hands sixty; and in the legs and feet sixty.
As the bones are the support of the animal fabric, I have inserted in the next page, a catalogue of the human skeleton, which occasionally may be referred to:
A Skeleton of the Human Body.
Bones in the Head.
The Skull.
The Forehead.
| Os Frontis | 1 |
The Hindhead.
| Os Occipitis | 1 |
The Sides of the Head.
| Ossa Parietalia | 2 |
The Temples.
| Ossa Temporum | 2 |
The Basis of the Skull.
| Os Ethmoides | 1 |
| Os Sphenoides | 1 |
The Bones of Hearing.
| Ossicula Auditus | 8 |
The Face.
The Upper-Jaw.
| Ossa Malæ | 2 |
| ——Maxillare | 2 |
| ——Unguis | 2 |
| ——Nasi | 2 |
| ——Palati | 2 |
| Os Vomer | 1 |
The Under-Jaw.
| Maxilla Inferior | 1 |
The Teeth.
| Dentes Incisivi | 8 |
| ——Canini | 4 |
| ——Molares | 20 |
The Tongue-Bone.
| Os Hyoides, is composed of | 3 |
| — | |
| 63 |
Bones in the Trunk.
The Spine.
| Vertebræ Cervicis | 7 |
| ——Dorsi | 12 |
| ——Lumborum | 5 |
The Ribs.
| Costæ Vera | 14 |
| ——Spuria | 10 |
The Shoulders.
| Scapula | 2 |
| Claviculæ | 2 |
The Hip and Bason.
| Os Sacrum, is composed of | 6 |
| Os Coxygis, is composed of | 3 |
| Ossa Innomenata, composed of | |
| ——Ischium | 2 |
| ——Ilium | 2 |
| ——Pubis | 2 |
The Breast.
| Sternum, is composed of | 3 |
| — | |
| 70 |
Upper Extremities.
The Upper Arm.
| Os Humerus | 1 |
The Under Arm.
| Ulna | 1 |
| Radius | 1 |
The Wrist.
| Ossa Carpi | 8 |
The Hand.
| Ossa Metacarpi | 4 |
The Fingers.
| Ossa Digitorum | 15 |
| — | |
| 30 |
Under Extremities.
The Thigh.
| Os Femoris | 1 |
The Knee Pan.
| Patella | 1 |
The Leg.
| Tibia | 1 |
| Fibula | 1 |
Ancle.
| Ossa Tarsi | 7 |
Foot.
| Ossa Metatarsi | 5 |
Toes.
| Digitorum | 14 |
| — | |
| 30 |
The connection of the bones are in various ways; those connections that are designed for rest, are by close contact of parts, and are called sutures or seams; such are the bones of the skull with themselves and the face. Those connections which are designed for motion are called articulation. Some of the articulations have but an obscure motion, as the ribs with the back-bone, and the back with itself, &c. Others have an angular motion, as the elbows and knees; and others again have an universal motion, as the arm-bone with the shoulder, and the thigh bone with the hip. The sutures, and such connections as have no motion, are merely dovetailed into one another in close connection; but those articulations that are designed for motion are connected by cartilages, either in close contact, or so as to move slippery over one another.
The ligaments are those tough tendinous parts, by which the articulations designed for motion are joined together; at some parts they cover the joints only, and at others, they are immediately fastened to each other, besides the external coverings; those ligaments are very strong and elastic, and have a close connection with the nerves that pass by them.
The surrounding ligaments of all moveable joints, form a capsular-bag, which contains a slippery liquor, called synovia, that lubricates the ends of the bones covered with cartilages, that they may move with ease and agility over one another.
Muscles are the fleshy parts on the human body, appointed for motion. They are a composition of arteries, veins, nerves, and tendons.
Muscles are generally divided into two kinds; those for necessary or involuntary motion, and those for voluntary. Some again are fastened at each end to some of the bones at their extremity, and contract themselves in a straight direction; others again are annular, or in the form of a ring; and by this manner open and shut. The first kind are generally divided into three parts, the head, belly, and tail. The whole muscle begins and ends in a tendon, by which it is fastened to the part it is designed to move; which, when the belly of the muscle contracts itself, must consequently draw both bones nearer together, fastened to the head and tail; and thus performs the motion. Some of these muscles act in consort, and others in opposition to each other.
The tendons are the principal parts of the muscle; and that part thereof, as before observed, which is fastened in the bones, namely, at the head and tail of the muscle, and is the chord, as it were, by which the limb is brought into motion.
A tendon is a hard, substantial, flexible, and elastic body, which, at the head of the muscle, is very compact; but as it enters the muscle, spreads its fibres over the whole body, gathers again at the tail, in as compact a manner as it began, and continues in this chord-like texture till it fastens itself at its appropriated place.[[7]]
[7]. It must be observed however, that tendons take on many various forms, as different as the muscles; which would be too tedious here to particularize.
The tendons and ligaments are of equal substance, and differ in nothing but their various uses; namely, the ligaments to connect the articulation; and the tendons, or the ends of the muscles, to give motion. The muscles are a composition of the tendinous fibres, plentifully intermixed with small ramifications of blood vessels; all which compose the fleshy part thereof. Hence, the tendons being white and hard, the muscles gradually grow softer and redder in the middle of them; and they verge gradually to become tendinous at the tail, the same as the head.
Hence, from the close texture of the tendons, they are very painful when wounded, or otherwise hurt; but as the muscles are softer and more pliable, their wounds and other accidents are of less consequence, and not so dangerous as the former.
The number of muscles are undetermined, for though the principal muscles are so distinct that they cannot be mistaken as to their form and use, yet there is so great a number of small ones, or so many of the great ones capable of being subdivided again, that anatomists have not, as yet, agreed about their number.