Figure Structure : Skeleton

Human newborns have over 270 bones some of which fuse together into a longitudinal axis, the axial skeleton, to which the appendicular skeleton is attached. The human skeleton is a collection of bones held together by ligaments, tendons, muscles and cartilage. The skeleton provides a framework for the body. It holds and protects the organs. It also provides a structure for the interconnecting muscles.

Many of the bones, such as the skull, vertebral column or spine, and thoracic cage or ribs are designed to transfer the weight of the head, the trunk, and the upper limbs down to the hip joint and lower limbs. this transfers the weight to the ground, and is responsible for maintaining the upright position of the body.

Many bones are connected at joints, where the bones are interconnected by muscles. These muscles allow the bones to move relative to each other, allowing us to walk, run and any other activity that involves movement of the body.

Axial skeleton

The axial skeleton (80 bones) is formed by the vertebral column (26), the rib cage (12 pairs of ribs and the sternum), and the skull (22 bones and 7 associated bones). The upright posture of humans is maintained by the axial skeleton, which transmits the weight from the head, the trunk, and the upper extremities down to the lower extremities at the hip joints. The bones of the spine are supported by many ligaments. The erectors spinae muscles are also supporting and are useful for balance.

Appendicular skeleton

The appendicular skeleton (126 bones) is formed by the pectoral girdles (4), the upper limbs (60), the pelvic girdle (2), and the lower limbs (60). Their functions are to make locomotion possible and to protect the major organs of locomotion, digestion, excretion, and reproduction.

Function

Support

The skeleton provides the framework which supports the body and maintains its shape. The pelvis, associated ligaments and muscles provide a floor for the pelvic structures. Without the rib cages, costal cartilages, and intercostal muscles, the heart would collapse.

Movement

The joints between bones permit movement, some allowing a wider range of movement than others, e.g. the ball and socket joint allows a greater range of movement than the pivot joint at the neck. Movement is powered by skeletal muscles, which are attached to the skeleton at various sites on bones. Muscles, bones, and joints provide the principal mechanics for movement, all coordinated by the nervous system.

Protection

The skeleton protects many vital organs.

The skull protects the brain, the eyes, and the middle and inner ears.
The rib cage, spine and sternum protect the lungs, heart and major blood vessels.
The clavicle and scapula protect the shoulder.
The ilium and spine protect the digestive and urogenital systems and the hip.
The patella and the ulna protect the knee and the elbow respectively.
The carpals and tarsals protect the wrist and ankle respectively.

Features of the Bones

The bones have a variety of knobs and hollows that provide for many different kinds of attachment.

Convex Forms

An eminence is the lowest kind of convexity - a flat bump.

A protuberance is a larger, roundish bump. A tubercle (TOO-ber-cul) is the same shape.

A tuberosity (too-ber-OSS-i-tee) is a high, elongated bump.

A process is a form large enough to jut out, often forming a finger-like shape.

A ramus (RAY-mus) is a flat branch of bone.

A spine is a long, sharp ridge.

A crest is a cliff-like edge.

A condyle (CON-dial) is a knob shape that faces the joints.

An epicondyle (ep-ih-CON-dial) is a bump near a condyle.

Concave Forms

A trochlea (TROK-lee-uh) is a spool-shaped form. A trochlea is shaped to receive a convexity at a joint and allow movement only through one plane.

A facet (fa-SET) is a shallow depression that recieves the convexity of another bone at a joint.

A fossa (FOSS-uh) is a hollow that is deeper than a facet.

A foramen (fuh-RAY-men) is a hole.

A groove is exactly that, a thin, linear depression.

Bony Landmarks

From person to person flesh varies more than bone. The skeleton, by comparison, offers a more stable set of reference points. Therefore artists are well served by becoming familiar with bony landmarks - points on the skeleton close to the skin that can be located by sight. By finding these landmarks, the positions of the bones can be determined, and the fleshy forms can be hung from them, as it were.

The spine has three bony landmarks: cervical vertebra #7, or C7 for short, and thoracic vertebra #12, or T12. Because of the way the cervical vertebrae sit on the ribcage, the neck pitches forward from C7; the whole head can be seen sitting forward from C7. Because of the mass of the ribcage, usually there's a shadow hanging around T12, where the two twelfth ribs connect. At the bottom of the spine is the sacrum, a wide bone that connects the spine to the pelvis.

The pelvis has three important landmarks. One is anterior superior iliac spine. ASIS looks like a complex term, but not upon examination: anterior means in front, and superior means higher (it sits directly above a smaller spine on the pelvis). The bone on this portion of the pelvis is the ilium (ILL-ee-um), hence iliac (ILL-ee-ack). A spine in this context is a little projection of bone.

The second is posterior superior iliac spine. The term has the same derivation, but since it lies on the back, it is posterior. PSIS sits under each dimple on the lower back, right above the buttocks.

The third is the pubic symphysis, where the bones of the pubic arch meet in the middle.

The ribcage has three landmarks. The supersternal (soo-per-STIR-nal) notch likes above the sternum, between the clavicles. There's a little hollow here at the base of the neck. At the other end lies the infrasternal notch, where the ribs meet the sternum. There's a hollow here as well. The third landmark is the low point of rib #10. This is the bottom of the ribcage when viewed from the front, because ribs #11 and #12 don't attach to the sternum. Rib #10 seems to rise up from this point towards the sternum and towards the back.

The scapula (SKAP-you-luh) has three landmarks. One is the acromion (uh-CROW-mee-on) process, the bony point of the shoulder. One is the spine of the scapula, which extends from the acromion to the medial side of the scapula. The third is the inferior angle of the scapula.

The leg has three. One the femur, the large bone of the thigh, is the great trochanter (TROW-kan-ter). This lies under the dimple on the hip when viewed from the side. Visible and palpable on either side of the knee are the condyles of the femur.

The lower leg has two bones. The tibia is larger and has two landmarks - the medial condyle, and the medial malleolus (mal-ee-OLE-lus), which is the medial bone of the ankle. The fibula is smaller, and has two landmark - the head, at the superior end, and the lateral malleolus, which is the bone of the ankle on the lateral side.

Between the femur and the tibia lies the patella (puh-TELL-uh), the kneecap, which is a landmark in its own right.

The humerus (rhymes with humorous), the bone of the upper arm, has two: the medial and lateral epicondyles, which can be seen and felt on either side of the elbow.

The ulna extends from the elbow to the pinky side of the hand. The point of the elbow is on the ulna, and is called the olecranon (oh-LECK-ruh-non). The head of the ulna is visible as a bump on the pinky side of the wrist.

The radius extends from the lateral condyle of the humerous (which is not a landmark, as it lies deep under the muscles of the arm) to the thumb side of the hand, where its styloid process is visible on that side of the wrist. It is worth noting that the ulna forms the axis of the lower arm; the radius is flipping around it as the forearm pronates and supinates. (Don't be fooled by the fact that the head of the ulna and the head of the radius are at opposite ends of the forearm. The heads of bones have a distinguishable common shape.)

The hyoid bone forms the corner of the neck. It's sitting at the top of the windpipe.

The skull has two landmarks useful for drawing the whole figure: the chin, and the occipital (ox-SIP-it-al) protuberance, a little projection of bone at the base of the skull.

Check out this link for a good video of the bony landmarks.
http://www.sophia.org/bony-landmarks-tutorial

Control Lines

These lines connect key points of the body in ways that don't usually occur to the beginner, but set up a framework to create form expediently. The control lines include some fleshy landmarks as well.

Spine Line