Human Rib-cage Anatomy

Ribs are not merely armour for the organs inside our torsos, as we reveal here…

The ribcage – also known as the thoracic cage or thoracic basket – is easily thought of as just a framework protecting your lungs, heart and other major organs. Although that is one key function, the ribcage does so much more. It provides vital support as part of the skeleton and, simply put, breathing wouldn’t be possible without it.

All this means that the ribcage has to be flexible. The conical structure isn’t just a rigid system of bone – it’s both bone and cartilage. The cage comprises 24 ribs, joining in the back to the 12 vertebrae making up the middle of the spinal column. The cartilage portions of the ribs meet in the front at the long, flat three-bone plate called the sternum (breastbone). Or rather, most of them do. Rib pairs one through seven are called ‘true ribs’ because they attach directly to the sternum. Rib pairs eight through ten attach indirectly through other cartilage structures, so they’re referred to as ‘false ribs’. The final two pairs – the ‘floating ribs’ – hang unattached to the sternum.

Rib fractures are a common and very painful injury, with the middle ribs the most likely ones to get broken. A fractured rib can be very dangerous, because a sharp piece could pierce the heart or lungs. There’s also a condition called flail chest, in which several ribs break and detach from the cage, which can even be fatal. But otherwise there’s not much you can do to mend a fractured rib other than keep it stabilised (usually by wrapping or taping), resting and giving it enough time to heal.

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What are hiccups?

Hiccupping – known medically as singultus, or synchronous diaphragmatic flutter (SDF) – is an involuntary spasm of the diaphragm that can happen for a number of reasons. Short-term causes include eating or drinking too quickly, a sudden change in body temperature or shock.

However, some researchers have suggested that hiccupping in premature babies – who tend to hiccup much more than full-term babies – is due to their underdeveloped lungs. It could be an evolutionary leftover, since hiccupping in humans is similar to the way that amphibians gulp water and air into their gills to breathe.

Breathe in, breathe out…

Consciously take in a breath, and think about the fact that there are ten different muscle groups working together to make it happen. The muscles that move the ribcage itself are the intercostal muscles. They are each attached to the ribs and run between them. As you inhale, the external intercostals raise the ribs and sternum so your lungs can expand, while your diaphragm lowers and flattens. The internal intercostals lower the ribcage when you exhale. This forces the lungs to compress and release air (working in tandem with seven other muscles). If you breathe out gently, it’s a passive process that doesn’t require much ribcage movement.

Ribs in animals

Most vertebrates (ie animals with backbones) have a ribcage of sorts -however, ribcages can be very different depending on the creature. For example, dogs and cats have 13 pairs of ribs as opposed to our 12. Marsupials have fewer ribs than humans, and some of those are so tiny they aren’t much more than knobs of bone sticking out from the vertebrae. Once you get into other vertebrates, the differences are even greater. Birds’ ribs overlap one another with hook-like structures called uncinate processes, which add strength. Frogs don’t have any ribs, while turtles’ eight rib pairs are fused to the shell. A snake’s ‘ribcage’, meanwhile, runs the length of its body and can comprise hundreds of pairs of ribs. Despite the variations in appearance, ribcages all serve the same basic functions for the most part: to provide support and protection to the rest of the body.

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Facts about ribs

True ribs – Rib pairs one through seven attach to the sternum directly via a piece of cartilage.

False ribs – Rib pairs eight through ten connect to the sternum via a structure made of cartilage linked to the seventh true rib.

Manubrium – This broadest and thickest part of the sternum connects with the clavicles and the cartilage for the first pair of ribs.

Sternal angle – This is the angle formed by the joint between the manubrium and the body, often used as a sort of ‘landmark’ by physicians.

Floating ribs – Pairs 11-12 are only attached to the vertebrae, not the sternum, so are often called the floating, or free, ribs.