Rib Cage

What Constitutes the Thoracic Basket?

The thoracic basket, also referred to as the thoracic cage, is the osseous framework that defines and safeguards the thoracic cavity and its internal organs. It possesses a conical form and bears resemblance to a birdcage, hence its name. This segment of the axial skeleton is situated in the chest region, above the abdominal cavity.

Functions

• The thoracic basket shields the two primary organs within the thoracic cavity – the heart and the lungs.
• It upholds the upper body, ensuring its stability.
• It serves as a point of fixation for the clavicles, establishing a connection between the arm and the axial skeleton.
• Due to its distinctive bony structure, it provides attachment points for a variety of muscles in the pectoral girdle and core stability muscles.
• It stabilizes the thoracic cavity through controlled outward and inward movements during inhalation and exhalation. 

Designation and Structural Composition of Bones in the Thoracic Basket

The human thoracic basket consists of 37 bones:

1. Sternum (1, singular): Also recognized as the breastbone, it is palpable at the center of the chest. This bone articulates with the first 7 ribs.
2. Thoracic vertebrae (12, singular): These comprise the 12 bones in the thoracic spine (T1-T12). Each vertebra articulates with its corresponding ribs to configure the thoracic basket. The primary function of the thoracic spine is to support and stabilize the rib cage.
3. Ribs (12, paired): These elongated, curved, flat bones enclose the anterior aspect of the thoracic basket. Out of the 12 paired bones, the first 7 pairs articulate with the sternum via their respective costal cartilages.

The space between two ribs is termed the intercostal space. With 12 pairs of ribs, there are 11 intercostal spaces on each side of the thoracic basket, with each space denoted by its position. For instance, the 1st intercostal space is positioned between the 1st and 2nd ribs. These spaces accommodate the intercostal muscles and aid in expanding the thoracic basket during inhalation.

The aperture at the lower end of the rib or thoracic basket is referred to as the inferior thoracic aperture or thoracic inlet. In contrast, the upper opening is known as the superior thoracic aperture or thoracic outlet. These two openings facilitate the connection of the organs within the thoracic basket with the external systems and structures.

Connections

1. Xiphisternal joint – Between the body of the sternum and xiphoid process
2. Manubriosternal joints – Between the body of the sternum and the manubrium
3. Sternoclavicular joints – Between the manubrium (upper part of the sternum) and the clavicles
4. Sternochondral joints – Between the sternum and the costal cartilage
5. Costochondral joints – Between the ribs and their costal cartilage
6. Costovertebral joints – Between the ribs and the bodies of the thoracic vertebrae.
7. Intervertebral joints – Between the 12 thoracic vertebrae
8. Interchondral joints – Between the costal cartilages.

Muscle Attachments

The following muscles are situated in the thoracic basket and contribute to its functionality: 

1. Intercostals (external, internal, and innermost layers)
2. Subcostals
3. Transversus thoracis

Sources

1. Thoracic basket: KenHub.com
2. The Thoracic Basket: Bones, Structure & Classifications: Study.com 
3. Thoracic Basket: What To Know: WebMD.com
4. Thoracic basket: Anatomy.app
5. The Thoracic Basket: OregonState.education