Torso Bones Anatomy

Front view of the human rib cage with the sternum and ribs.

The torso contains the thoracic, abdominal, and pelvic cavities, supported and enclosed to varying degrees by bones and muscles.

These cavities are:

Thoracic cavity;
Abdominal cavity;
Pelvic cavity.

Human torso showing the thoracic, abdominal, and pelvic cavities.

The skeleton surrounding the thoracic cavity is formed by the thorax, or rib cage. The pelvic skeleton is formed by the pelvic bones, sacrum, and coccyx.

We will analyze the pelvic bones in a separate article about the lower limbs. The abdominal cavity has no complete bony enclosure, although the spine and lower ribs provide support and partial protection.

Rib Cage

The rib cage is a strong bony framework that surrounds much of the thoracic cavity. The thoracic wall consists of the rib cage and associated muscles. The lungs are enclosed by pleural membranes, with the parietal pleura lining the inner surface of the thoracic wall.

The rib cage protects important organs and tissues of the thorax, including the heart and lungs, as well as major blood vessels. The lower ribs also provide partial protection for organs of the upper abdomen, especially the liver and spleen.

The rib cage has the general appearance of a truncated cone. The upper and lower openings of the thorax are called the superior and inferior thoracic apertures.

Rib cage showing the superior and inferior thoracic apertures.

The inferior thoracic aperture is largely closed by the diaphragm, a powerful muscle involved in breathing that separates the thoracic and abdominal cavities.

The rib cage does more than protect internal organs. The movable joints between the ribs, vertebrae, and sternum allow the thorax to expand during inhalation and become smaller during exhalation.

So, the rib cage is formed by the sternum, ribs, and vertebrae of the thoracic spine.

Sternum

The sternum is a flat, sturdy bone located at the front of the rib cage. The costal cartilages of the true ribs connect to the sternum. This is where the sternum is located:

The sternum has three main parts: the manubrium, body (corpus sterni), and xiphoid process. Along its sides are costal notches (incisurae costales) for articulation with the costal cartilages.

The sternum also helps connect the upper limbs to the axial skeleton because the clavicles articulate with the manubrium. You can see the clavicular notches (incisurae claviculares) on the manubrium.

Sternum anatomy with the manubrium, body, xiphoid process, and costal notches labeled.

Ribs

A rib is a flat, curved bone that articulates posteriorly with the thoracic vertebrae. Each person normally has 12 pairs of ribs. Ribs 3 through 9 are considered typical, while ribs 1, 2, 10, 11, and 12 have anatomical features that distinguish them from the typical ribs.

Each rib has a bony part and a costal cartilage. The bony part makes up most of the length of the rib. In this illustration, the cartilaginous parts of the ribs are colored blue, while the bony parts are not colored.

Rib cage showing the ribs and costal cartilages from the front.

A typical rib has a head (caput costae), neck (collum costae), tubercle, and body (corpus costae). The head of the rib articulates with the bodies of the thoracic vertebrae, while the tubercle articulates with a transverse process.

Typical rib anatomy with the head, neck, tubercle, and body labeled.

The first seven pairs of ribs attach to the sternum through their own costal cartilages and are therefore called true ribs.

The next three pairs connect indirectly to the sternum because their costal cartilages join the cartilage above, forming the costal margin. These are false ribs. The lowest two pairs are called floating ribs because their anterior ends do not attach to the sternum or costal margin.

The right and left costal margins form the infrasternal angle below the xiphoid process. This area is important in plastic anatomy because its width influences the visible shape of the lower rib cage.

In traditional constitutional descriptions, people with a broad, stocky build tend to have a wider infrasternal angle, while people with a narrow, slender build tend to have a more acute angle.

These differences can be useful to observe when drawing different body types, but they vary from person to person and should not be treated as fixed rules.

Three human figures showing different shapes of the infrasternal angle.

The thoracic vertebrae are also part of the rib cage. We will now look at the thoracic spine as part of the vertebral column.

Spine (Vertebral Column)

The vertebral column is the main supporting axis of the trunk. It supports the head and torso, protects the spinal cord, and provides both stability and mobility.

The vertebral column usually consists of 33 vertebrae, although the number of coccygeal vertebrae can vary. Between most adjacent vertebral bodies are intervertebral discs made of fibrocartilage.

Together with the joints, muscles, and ligaments of the spine, these discs allow the vertebral column to remain strong and flexible while absorbing loads during movement.

The vertebral column is divided into several regions:

Cervical (7 vertebrae);
Thoracic (12 vertebrae);
Lumbar (5 vertebrae);
Sacral (5 fused vertebrae);
Coccygeal (usually 4 fused vertebrae, although the number can vary).

Vertebral column showing the cervical, thoracic, lumbar, sacral, and coccygeal regions.

The vertebral column is not straight when viewed from the side. It has four normal curves that help support the body and distribute mechanical loads.

The cervical region curves forward. This curve is called cervical lordosis.

The thoracic region curves backward. This curve is called thoracic kyphosis.

Below this is the forward curve of the lumbar region, called lumbar lordosis. The sacral region curves backward, forming sacral kyphosis.

Side view of the vertebral column showing lordosis and kyphosis.

Let’s analyze the anatomy of a typical thoracic vertebra.

Thoracic Vertebra

The thoracic vertebrae are larger than the cervical vertebrae, and their bodies generally increase in size as they approach the lumbar region.

A thoracic vertebra has a vertebral body (corpus vertebrae) and a vertebral arch (arcus vertebrae), which together enclose the vertebral foramen (foramen vertebrale). When the vertebrae are stacked, these foramina form the vertebral canal, which contains the spinal cord.

The spinous processes (processus spinosi) of the thoracic vertebrae are generally long and directed downward, especially in the middle of the thoracic region. Some overlap like roof tiles. The spinous processes can be visible beneath the skin, especially in thin people.

Thoracic vertebra anatomy with the body, vertebral foramen, and processes labeled.

Thoracic vertebrae also have superior and inferior articular processes, which form joints with adjacent vertebrae.

A characteristic feature of the thoracic vertebrae is that they articulate with the ribs. For this purpose, the vertebral bodies and transverse processes have costal facets.

Typical thoracic vertebrae have superior and inferior costal demifacets on the sides of their bodies. The head of a typical rib articulates with the corresponding vertebra and the vertebra above it.

The first thoracic vertebra has a complete facet for the first rib and an inferior demifacet for the second. The lower thoracic vertebrae differ from this typical pattern, with T10, T11, and T12 generally having a single complete costal facet for the corresponding rib.

The superior and inferior vertebral notches are located along the pedicles of adjacent vertebrae. Together, these notches form the intervertebral foramina through which spinal nerves pass.

Side view of a thoracic vertebra with the body, facets, and processes labeled.

On most thoracic vertebrae, the transverse processes also have transverse costal facets (foveae costales processus transversi), which articulate with the tubercles of the ribs. These facets are absent on T11 and T12.

Lumbar Vertebra

The lumbar vertebrae are the largest vertebrae in the movable part of the spinal column because they bear a substantial portion of the body’s weight.

Human skeleton showing the lumbar region of the vertebral column.

You can compare the sizes of the cervical, thoracic, and lumbar vertebrae:

Comparison of cervical, thoracic, and lumbar vertebrae.

Each lumbar vertebra, like the vertebrae described above, has a vertebral body (corpus vertebrae), a vertebral arch (arcus vertebrae), and a vertebral foramen (foramen vertebrale) enclosed between them.

The spinous process (processus spinosus) is short, thick, and broad compared with the longer, more downward-directed spinous processes of the thoracic vertebrae.

Lumbar vertebra anatomy with the body, vertebral foramen, and main processes labeled.

Superior and inferior articular processes (processus articularis superior and inferior) extend from the vertebral arch. These processes form joints between adjacent vertebrae.

The lumbar vertebrae have long lateral projections known as costal processes. These correspond developmentally to the costal elements of the vertebrae and form the main lateral projections of the lumbar vertebrae.

Side view of a lumbar vertebra with the body and articular processes labeled.

The skeleton of the trunk also includes the pelvic bones, which support the lower part of the trunk. The pelvic bones are discussed separately in our article about the anatomy of the lower limbs.

Drawing a skeleton is a difficult task. A common mistake among aspiring artists is paying too much attention to small details before establishing the basic forms.

First, learn to sketch the overall shape of the rib cage and spine. Add smaller features such as the spinous processes and costal cartilages only after you feel confident with the larger forms.

Drawing the spine and rib cage correctly is especially important because their forms strongly influence the overall shape of the torso. Errors in the placement and form of these bones can affect the construction of the entire human figure.