The Influence of Bones and Muscles on Form

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The Influence of Bones and Muscles on Form

Dover Publications, Inc.

The Bones

Table of the Bones.

The following table constitutes a reference and will help the memory, as regards the names of the bones, and their position in the skeleton; it also gives the number of bones in each great subdivision of the body, as well as the total number in the whole skeleton. The shoulder-girdle and hip-girdle are here placed in conjunction with their respective extremities. The two patellae are not enumerated as bones of the skeleton proper; nor are certain little ossicles, six in number, belonging to the ears, though these latter deserve to be so considered.

The long bones are always curved. Some, like the femur, present a single curve; others are curved in two directions, like the collar-bone, while others, again, like the ulna and the ribs, present complex curves, accompanied often with a twist or torsion. All such curvatures increase the elasticity and, so far, the resisting power of the bone; they also serve to enlarge the surface of attachment for muscles, and to furnish the means of giving special direction to certain portions of a muscle.

REFERENCE LETTERS SAME AS PROFILE

THE MALAR BONES

The malar bones or cheek bones, are the two thick, irregularly quadrangular bones, which underlie the prominent portion of the cheeks, and which become so plainly discernible in emaciated persons; they also pass backwards, to assist in forming the zygomatic arches, and likewise complete the floor, the outer wall, and the outer border of the orbit.

Each malar bone consists of a central part or body, of an orbital plate, and of three processes, one running upwards, one backwards, and one forwards. The body of the bone is prominent on its outer side, where it forms the malar eminence, which is broad, unevenly convex and partly subcutaneous; it is crossed by a nearly horizontal ridge, which divides it into a narrower lower surface, giving origin to the two zygomatic muscles and, in front of these, to the levator labii superioris, and a broader upper surface, somewhat depressed, which becomes continuous with the superior process of the bone. This superior or frontal process, is the broadest and longest of the three; it ascends to join, by a jagged surface, the external angular process of the frontal bone, to complete the outer border of the orbit, and to unite the cranium and the face. This part of the orbital border is incurved, so as, with the depression in the adjacent part of the body of the bone, to increase the range of vision in the outward and downward direction; upon this portion of the malar bone, the orbicularis palpebrarum muscle rests.

THE SUPERIOR MAXILLARY BONES

These two large bones, right and left, are united in the middle line to form, as their name implies, the upper jaw. They are placed almost vertically beneath the frontal bone, except in the Black races. As compared with animals, this position of the maxillary bones is characteristic of man; and so, likewise, is their relatively small size. They support the malar bones on each side, form part of the floor, lower border and inner side of the orbits, have the nasal bones attached to them in front, bound the anterior nasal openings on the sides and below, and support the upper teeth. Behind and within the dental arch, their deepest parts form the fore part of the hard palate.

The diligent Anatomist can demonstrate the relations between Reality and Beauty; but, on the Sculptor and Painter, devolves the higher task of detecting their joint significance, and realizing their combination in the creations of Art. This goal may be attained by the rough, but open, road of individual experience, or, after groping through the fog of ignorance, or escaping from the mazes of error; or it may be reached, almost unconsciously, by the possessor of Nature's rarest gifts. But in this, as in all other callings, to the few, as well as to the many, the path of Knowledge is the shortest and clearest avenue by which such a goal can be approached.

THE INFERIOR MAXILLARY BONE

This bone, the lower jaw bone, or mandible, J?, is the largest and strongest in the face. Originally composed of two symmetrical halves, it very early becomes a single bone, by the union of these vertically along the middle line, forming the symphysis. It is shaped somewhat like a horse-shoe with the open ends directed backwards and turned sharply up. In regard to length, it is adapted to meet the upper jaw bone; being used only for purposes of mastication and speech, and not for seizing food or prey, both jaws are comparatively short. The thick, solid, horizontal part, which supports the inferior dental arch, containing the lower teeth, is named the body, and the upturned, flattened ends, the rami or branches. The under border of the body meets the hinder border of the ramus, on each side, at the rounded angle, a very important point in relation to the width and form of the cheek.

The horizontal portion of the bone, below and in front of the curved line and the occipital protuberance, is concealed by the muscles of the neck, and does not influence the surface forms; but, nevertheless, it must be described, as forming the part of the cranium which articulates with the first cervical vertebra. In it, is the foramen magnum, f, a large, oval aperture, with sloping margins, having its long axis directed from before backwards, and its plane nearly horizontal, which leads upwards into the cranial cavity, corresponds with the vertebral canal, below, and gives passage to the spinal cord, as this passes down from the brain. On the sides of the foramen magnum, are the right and left occipital condyles, c', articular processes, which are received into, and rest upon, the two cup-shaped upper articular surfaces of the atlas. Like these surfaces, the occipital condyles are ear-shaped, being slightly incurved on their inner, and rounded on their outer, border; they are situated nearer to the front of the foramen magnum, and converge slightly forwards.

THE MOVABLE VERTEBRÆ. THE MOVABLE PART OF THE VERTEBRAL COLUMN.

The lower, immoveable part of the vertebral column or spine, consisting of the sacrum and the coccyx, having been described as parts of the pelvis, it remains here to examine the upper, moveable part, extending from the base of the sacrum to that of the skull, occupying the regions of the loins, back, and neck, and consisting of twenty-four vertebræ, lumbar, dorsal, and cervical, such set being numbered from above downwards, namely, the first to the seventh cervical, the first to the twelfth dorsal, and the first to the fifth lumbar. They are arranged one upon the other, and held together, so as to form a strong, curved, flexible, elastic column. In the natural skeleton, they are chiefly connected by a series of interposed fibro-cartilaginous discs, the intervertebral substances, replaced, in the artificial skeleton, by discs of cork, covered with leather.

Each vertebra consists of several parts. Of these a central massive part, directed forwards, is named the centrum, centre, or body; behind this, is an arch, the so-called neural arch, composed of two equal and lateral halves, right and left, each of which again consists of a short piece, next to the centrum or body, called the pedicle, and of a longer piece, reaching from this, backwards and inwards, to the middle line, named the lamina. The body and, the arch together form a ring, which surrounds a large open space, the spinal or vertebral foramen;, this forms part of the spinal or vertebral canal.

THE SCAPULA

The scapula or shoulder-bones proper, the two remarkable, broad, flat, thin, triangular bones, which are articulated to the outer ends of the clavicles, are also suspended by various muscles, which reach them from the trunk, and even from the head. They form the outer and the posterior prominences of the shoulder, being placed, like two wings, on the back of the thorax, covering a space, on each side, extending, longitudinally, from near the first, to a little below the seventh rib, and, transversely, from just outside the angles of the ribs, beyond the sides of the thorax, to the back and upper part of the arm-pits, where they furnish the sockets for the arm-bones. As the deep surface of the scapula is not so concave as the thorax is convex, this bone, especially at its upper and outer part, is removed a short distance from the thoracic walls.

The Shoulder Girdle; The Clavicle and The Scapula.

THE CLAVICLE

The clavicles or collarbones, the well-known bones which pass across the front of the upper part of the thorax, and the lower part of $he neck, are placed nearly horizontally, one on each side, between the top of the sternum, just above the first costal cartilage and rib, and the acromion process of the scapula. They are, however, not strictly horizontal, but nearly always, when the shoulders are held in their ordinary position, a little higher at their outer ends. If the shoulders are allowed to drop, then the collarbones may become more nearly horizontal. When, on the other hand, the arms are raised, especially above the horizontal line, the collar-bones assume an oblique direction. The collar-bones do not pass directly outwards from the sternum, but outwards and somewhat backwards. Moreover, their inner ends do not reach the middle line of the body; neither do their outer ends extend so far as to constitute the extreme point of the shoulder girdle; for the acromion process of the scapula, on each side, lies beyond them, and really forms the outermost point of this portion of the trunk.

THE STERNUM, OR BREAST-BONE

This flattened, median bone fits in between the cartilages of the upper seven ribs, so as to close in the chest, in front. It also serves to support the clavicles above, and consequently furnishes a base of support for the upper limbs. The entire bone has been compared to a short, straight sword, like a Roman sword, and its lower, middle, and upper parts, have been named, respectively, the point, the blade, and the handle.

The Bones of the Thorax. The Ribs, Costal Cartilages, and Sternum.

The thorax or chest, has for its osseous and cartilaginous framework, the twelve dorsal, rib-bearing vertebræ behind, the twenty-four ribs with their cartilages, at the sides, and the sternum or breast-bone in front. The ribs not only form the sides of the thorax, but assist in completing its walls, both in front and behind.

THE AXIS AND ATLAS

These vertebræ, the second and the first cervical, are thus modified. The body of the second cervical vertebra, is somewhat deeper in front, from above downwards, than the one below it, and its upper surface is not flattened for the attachment of an intervertebral disc, to connect it with the under surface of the vertebra above, but, on the contrary, is prolonged upwards, in the form of a very strong toothed-shaped process, named the odontoid, or dentate process (dens; a tooth), the vertebra itself being designated the vertebra dentata.

The first cervical vertebra, or atlas, so named because it supports the head, as the hero Atlas supported the earth.

The size and shape of the several component parts of a vertebra, necessarily vary, as the uses to which they are put, are modified in each region of the spine. There is, however, no sudden change, but rather a transition, from one form of vertebra to another, at the limits of the different regions, and the middle vertebræ of each region are typical of that region. Nevertheless, the twelve dorsal vertebræ are quite peculiar, in being connected each with a pair of moveable ribs; and the cervical vertebræ, with the exception of the lowest, are distinguished by having their transverse processes perforated at the base.

The centra or bodies of the vertebræ may be said, in general terms, though the statement requires to be accepted with reserve as regards the dorsal region, to diminish in size from the lower to the upper end of the column, more especially in their height and transverse sectional area. This is in evident relation to the proportionately diminishing weight which they have to carry. In the lumbar region the bodies are much the largest in all their dimensions; their broad under and upper surfaces are oval or somewhat kidney-shaped, and much widened transversely. This part of the spine, being unsupported at the sides by ribs, possessed of a considerable range of movement, and capable of much lateral inclination, requires special support in that direction. The lumbar bodies, moreover, are relatively more constricted across their middle, so as to project considerably at their upper and under margins; they are, likewise, thicker, from below upwards, in front than at the back, thus assisting in the production of the lumbar spinal curve, which is convex anteriorly. This peculiarity is especially noticeable in the body of the fifth or lowest lumbar vertebra, the under surface of which is very oblique, to fit the slanting upper surface of the sacrum, just above its promontory, opposite the sacro-vertebral angle. In the dorsal region, the bodies diminish in size up to the fourth vertebra, above which they again increase up to the first.

In the cervical vertebræ, the bodies, speaking generally, are smaller than those of the back, the weight to be carried by them being less. Their transverse is in excess of their antero-posterior diameter, thus providing the required support, in lateral inclination of the neck, which is sometimes very considerable. The bodies of the lower five cervical vertebræ have, moreover, their upper surface shaped, from before backwards, like a shallow gutter, bounded on each side by a well-marked elevated lip, the surface of the vertebra next above, being bevelled off at each side, so that it fits into the recess on the one below. This peculiarity, which also exists on the upper surface of the body of the first dorsal vertebra, renders safer the free movements of this part of the vertebral column. The cervical bodies are rather thicker in the vertical direction in front, than at the back, in correspondence with the cervical curve, which is convex anteriorly. Not only the bodies, but all the other parts of the second and first cervical vertebræ, are so modified, that they will require special description.

The deficient height of the female pelvis, as compared with that of the male, and its less massive form, are well seen, also, in a side view.

The most numerous and remarkable differences between the skeleton of the male and female, however, are to be found in the pelvis.

Regarded from the front or behind, the female pelvis, is wider, but vertically shorter or more shallow than the male, which is narrow, and long or deep. All its parts are smoother, lighter, and necessarily weaker, in the female; the alæ of the iliac bones are thinner, broader, flatter, and more expanded, the crests of the ilia are longer but shallower, not rising up so high; they are also further apart, so that the average extreme width from one crest to another, is greater, though their height is less.

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Excerpted from The Influence of Bones and Muscles on Form by Walter T. Foster. Copyright © 1931 Dover Publications, Inc.. Excerpted by permission of Dover Publications, Inc..
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