Recently, I was asked a question I have been asked many times before. ‘How long is a giraffe’s neck and how many bones does it have?’
My standard response is to answer, ‘Depends how tall the giraffe is!’
But the facts have started to come back to me, taking me back to when I was at school and when I learnt to be a guide. The number of vertebrae in a giraffe’s neck is exactly the same as that in a human neck. Like us, they have seven cervical vertebrae, but each is much longer than the human equivalent; giraffe vertebrae are 25 cm in length. The fascinating thing is that between each of the giraffe’s vertebrae there is a ball-and-socket formation that gives the neck elasticity and enables the animal to move in a smooth and fluid motion. The ball and socket allow it to extend its head to an almost vertical position, a skill not possessed by other creatures.
Let’s look at the giraffe’s neck in detail. It can be up to 2 m in length, depending on the height of the animal when fully grown. The neck accounts for almost a third of the giraffe’s height. At this point the articulation between the cervical and thoracic vertebrae of the giraffe is shifted to lie between the first and second thoracic vertebrae, allowing more flexibility and giving added stability. In other ruminants, this point usually lies behind the seventh cervical vertebrae.
The neck comprises 52–54% of the giraffe’s entire vertebral column; in other mammals this ratio is 27–33%. The elongation takes place largely after birth, as giraffe mothers would have a difficult time giving birth to young with the same proportions present in adults. So, in short, the giraffe’s neck is approximately one-third of the giraffe’s height.
When looking at a giraffe, you may have noticed a slight hump at the base of its neck, above its shoulders. This protrusion is created by the tension caused by the muscles, tendons and ligaments that support the neck.
Another fascinating fact is that giraffes don’t experience a rush of blood to the head when they bend down to drink. This is because the animal has non-returnable valves in its main arteries. With a blood supply that can weigh 10 kg, the giraffe’s body has to generate about double the normal blood pressure of a large mammal in order to counteract gravity and maintain the flow to the brain. The non-returnable valves in the upper neck and complex pressure-regulation system, called the rete miribale, prevents excess blood flowing to the brain when the giraffe lowers its head to drink. The blood vessels in the lower legs are under greater pressure because of the weight of the fluid pressing down on them. In other animals, such pressure would force blood out to the capillary walls. In the giraffe, however, a very tight sheath of skin over the lower limbs maintains high pressure on the vascular system – it works in exactly the same way as the protective suit worn by a pilot to counteract G-force.