The rib cage functions as a bony shield, safeguarding the heart, lungs, and major blood vessels within the thoracic cavity. Understanding the geography of these protective bones is a fundamental skill for anatomical awareness. The ribs also play a functional role, moving with the diaphragm and intercostal muscles to facilitate the mechanics of breathing. Learning to locate and count these structures using surface anatomy provides a practical way to map the chest area.
Anatomical Overview of Rib Classification
The human body typically contains 12 pairs of ribs. These ribs are categorized into three groups based on their connection point at the front of the body. The first seven pairs are designated as true ribs, because each one attaches directly to the sternum, or breastbone, via its own piece of costal cartilage.
The next five pairs, ribs 8 through 12, are known as false ribs because they do not connect directly to the sternum. Ribs 8, 9, and 10 attach indirectly, with their costal cartilage joining the cartilage of the rib immediately above it, eventually connecting to the sternum through the seventh rib’s cartilage. Ribs 11 and 12 are a special subset of false ribs often called floating ribs, as they are not connected to the sternum or to any other rib’s cartilage at all. Instead, their anterior ends are free, offering protection for structures like the kidneys in the posterior abdominal area.
Locating the Sternal Angle to Identify the Second Rib
Accurate rib counting begins with locating a single, identifiable landmark on the front of the chest. Start by finding the suprasternal notch, the dip felt at the top center of the sternum. Slide your fingers straight down the sternum a short distance from this notch.
As you move down, you will encounter a slight, horizontal ridge or elevation known as the sternal angle (Angle of Louis). This bony prominence represents the junction between the manubrium and the body of the sternum. This angle is a consistent marker because it correlates directly with the second costal cartilage. By moving your finger laterally away from the sternal angle, you will immediately feel the second rib (R2).
Step-by-Step Palpation Technique for Counting
Once the second rib is identified using the sternal angle, it becomes the starting point for counting the remaining ribs in sequence. With a finger resting on the second rib, slide it down until it drops into the soft space directly beneath that rib. This space is the second intercostal space, named for the rib superior to it.
The next hard, bony structure encountered below the intercostal space will be the third rib (R3). Consistently follow this pattern—finding the rib, sliding down into the intercostal space, and identifying the next rib—to count down the chest wall. This method is effective for counting the true ribs, typically down to the seventh rib.
To find the floating ribs (ribs 11 and 12), you must move your palpation to the sides and back, as they do not extend to the front of the body. These lowest ribs can be felt as short, free-ending structures just above the waistline.