The Skeletal System And Movement

Every artist who wants to do figure drawing must first learn about the skeleton—the shape and placement of the skull, rib cage, pelvis, and scapula as well as the rest of the bones of the extremities. Every curve, bump indentation, and bulge in the body is superimposed on the underlyin bones, and life-drawing instructors could hardly conceive of a better way t start their courses than to ask students to draw a skeleton covered wit translucent plastic shrink-wrap—-just skin and bones. Looking within sue a model, students would see two distinct skeletal units: the appendicuk skeleton and the axial skeleton. The former refers to the bones of th appendages (the upper and lower extremities), and the latter refers to tf bones that lie in the central axis of the body—the skull, the vertebral eolum and the rib cage, including the sternum. The appendicular skeleton, as tl name suggests, is appended to the axial skeleton—the upper extremiti are attached to the sternum at the sternoclavicular joints, and the low r extremities are attached to the sacrum at the sacroiliac joints. Tak i together, the two units form the frame upon which the entire body is organic I.

(Technical note: ft is noteworthy and perhaps surprising to many that the p

.joints, which are the sites for flexing, extending, and rotating the thighs, do >t form axial-appendicular junctions. The reason is simple: both the femur and ie pelvic bone are part of the appendicular skeleton, and it is the pelvic bone alone i it articulates with the axial skeleton.]

We'll discuss the skeletal system and movement in more detail, but f it we need to review some common anatomical terms that we'll be us lg routinely from this point on. "Anterior" refers to the front of the b< f, "posterior" refers to the back of the body; "lateral" refers to the si e; "medial" means toward the midline; "superior" means above; "inferi r" means below; "proximal" means closer to the torso; and "distal" me is away from the torso. Sagittal planes lie from front to back, top to botl< n; the one and only midsagittal plane is the sagittal plane that bisects ie body in two right-left halves, and parasagittal planes include all sagi al planes that are lateral and parallel to the midsagittal plane. The corona >r frontal planes lie from side to side, top to bottom, such as a plane that ri is through the ears, shoulders, torso, and lower extremities. The transversa >r cross-sectional planes lie from side to side, front to back (fig. 4.2).

I STANDING POSTCRhS 211

the appendicular skeleton

The appendicular skeleton for the lower extremities forms the foundation for standing postures. From top to bottom, it includes the pelvic bones, the femur, patella, tibia, fibula, and the bones of the ankles and feet (fig. 4.3J. The pelvic bones and the sacrum comprise the pelvic bowl (figs. 2.8, 3.2, and 3.4), which is thus an axial-appendicular combination of three bones. The femur is the single bone in the long axis of the thigh, and the patella is the "kneecap." The tibia and fibula are in the leg. The anterior border of the tibia—the shin—is familiar to everyone as the front surface of the leg that is so vulnerable to painful bumps and bruises. The fibula is located laterally, deep to the calf muscles. The tibia and fibula remain in a fixed position parallel to one another, the tibia medial to the fibula from top to bottom. The bones of the ankle and foot include the tarsals, metatarsals, and phalanges.

The appendicular skeleton for the upper extremities is used for manipulating objects in our environment and is often an important accessory for bracing difficult standing poses. The bones of the upper extremity include

Appendicular Skeleton

ANATOMY Of HATHA YOGA

left clavicle left scapula right forearm is partially prorated left humerus left torear is supinai

ANATOMY Of HATHA YOGA

left clavicle left scapula left humerus left torear is supinai right forearm is partially prorated

Figure 4.3. The appendicular skeleton \f> defined as all the bones «if the upper and lower extremities, including the pelvic bones, scapulae, and clavicles-

Yoga For Skeletal Movement

in the feet and ankles: tarsals, metatarsals, and phalanges

Figure 4.3. The appendicular skeleton \f> defined as all the bones «if the upper and lower extremities, including the pelvic bones, scapulae, and clavicles-

in the feet and ankles: tarsals, metatarsals, and phalanges

1. STANDING POSTVRfS 213

the clavicle (the collarbone), the scapula (the shoulderblade), the humerus, radius, ulna, and bones of the wrist and hand (fig. 4.3). The clavicle is the only bone of the upper extremity that forms a joint (the sternoclavicular joint) with the axial skeleton. It also happens to be the most commonly broken bone in the body. If you fall on the point of your shoulder, the dead weight of your upper body can snap the clavicle like a diy branch.

The humerus is the single hone of the arm, and the radius and ulna are the two bones of the forearm. If you stand upright, palms facing forward in the "anatomical position," the radius and ulna are parallel, with the ulna on the medial side near the hips and the radius on the lateral side. This position for the forearm is called supination-, its opposite is pronation. You supinate your right forearm when you drive a wood screw into a plank clockwise. If you rotate the same screw out of the plank, turning your right hand counter-clockwise, you are pronatingthe forearm. During pronation the radius and ulna shift to form a long, skinny X so that the distal part of the radius is rotated to an inside position, and the distal part of the ulna is rotated to an outside position. Here (fig. 4.3) the left forearm is shown supinated and the right forearm is shown partially pronated. The bones of the wrist and hand include the carpels, metacarpels, and phalanges.

the axial skeleton

The axial skeleton forms the bony axis of the body (fig. 4.4). In addition to the vertebral column (the spine), it includes the skull, the rih cage, and the sternum, or breastbone. Looking at the vertebral column from its right side reveals that the spine forms a reversed double S, with one reversed S on top of the other (viewed from the left side, envision a plain S on top of the other). The top curve faces right, the next one left, the third one again right, and the bottom one again left (figs. 4.ioa-b). This reversed double S represents the four curves of the vertebral column. From the top down, the first and third convexities face anteriorly, and the second and fourth convexities face posteriorly. These are also the sites of the four main regions of the vertebral column: cervical, thoracic, lumbar, and sacral (figs. 2.29a-e, 4.4, and 4.10). A curve facing anteriorly is a lordosis, and a curve facing posteriorly is a kyphosis. The curves alternate: cervical lordosis, thoracic kyphosis, lumbar lordosis, and sacral kyphosis. Each region contains a specific number of vertebrae: seven in the cervical region (C1-7), twelve in the thoracic region (T1-12), and five in the lumbar region (L1-5). The sacrum is a single fixed bone.

In the fetus the entire spine is curved posteriorly, as mimicked by the child's pose (or fetal pose) in hatha yoga (fig. 6.18). When an infant begins t° crawl, and later walk, secondary curvatures that are convex anteriorly— the cervical lordosis and lumbar lordosis—develop in the neck and lumbar

214 ANATOM* OH HATHA Y(K,A

sacrum and coccyx (kyphosis)

-.j rib cage and sternum thoracic vertebrae (kyphosis)

cervical vertebrae (lordosis)

spinous process. 7th cervical vertebra

Figure 4.4. The axial skeleton includes the vertebral column, skull, rib cage, and sternum.

Yoga For Skeletal Movement

sacrum and coccyx (kyphosis)

-.j rib cage and sternum thoracic vertebrae (kyphosis)

Figure 4.4. The axial skeleton includes the vertebral column, skull, rib cage, and sternum.

cervical vertebrae (lordosis)

spinous process. 7th cervical vertebra lumbar vertebrae *-.'."' (lordosis)

regions, while the posterior convexities—the thoracic kyphosis and the sacral kyphosis—are retained in the adult. The four curvatures act together as a spring for cushioning the upper body from the impact of running and walking. In standing postures the curvatures are easy to keep in their optimal configuration, neither too straight nor too pronounced, but in cross-legged meditative sitting postures the lack of hip flexibility makes this more challenging.

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Responses

  • jukka-pekk
    What does sagial plane mean?
    6 years ago
  • marcel
    Are extremities, ribs, sternum and sacrum a part of the axial skeleton?
    6 years ago
  • agenore
    Why the appendicular skeleton called appendicular skeleton?
    6 years ago

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