MadSci Network: Zoology |
There are many ways to approach this question, and since my speciality is human anatomy, I’m going to approach it asking why are cats more flexible than humans? or why aren’t humans very flexible?
The answer to this question comes down to a study of the vertebral column. Click here for information on the cat\222s vertebrae. The basic body plan calls for 5 types of vertebrae – neck (cervical), chest or the ones that have ribs (thoracic), lower back (lumbar), attachment to the pelvis (sacrum), and tail (caudal in most mammals, coccygeal in humans).
All mammals (or almost all) have seven cervical vertebrae. This allows us to bend our head side-to-side or forward-and-backward or to turn our head to the left and right. Because we both have seven cervical vertebrae cats and humans have about the same flexibility in the neck.
The thoracic vertebrae hold the ribs, which protect the internal organs. Because the ribs tend to restrict movement there is not a lot of room for differences in flexibility here.
I’ll save the lumbar vertebrae for last, and move onto the sacrum. The role of the sacrum is to attach the body to the lower (or hind) limbs. The bones of the sacrum typically fuse together, and so they tend to prevent movement. Therefore, although humans have more sacral vertebrae than cats do, there is not much difference in their flexibility here.
The human tail (the coccyx) is very short and contains only 4 rudimentary bones. In humans the coccyx is used primarily for muscle attachment. Cats have a much longer tail with many more vertebrae, so a cat’s tail is more flexible because there are more bone here.
Now back to the lumbar vertebrae. Humans typically have five lumbar vertebrae and cats typically have seven. So, just for that reason alone, we would expect cats to be slightly more flexible. But there is more to it. Because of the human upright posture, the lumbar vertebrae must support and transmit the body weight to the lower limbs. This means that the human lumbar vertebral column must be able to limit unwanted movements. In the cat, the lumbar vertebrae do not need to support much body weight. Instead, the cat uses them as a "spring" while galloping, or pouncing, after prey. The lumbar vertebrae then become an important part of the locomotor system that allow the cat to move farther and faster.
So, cats are more flexible largely because they have more lumbar vertebrae and because their vertebrae are built to enhance speed of running rather than to support body weight.
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