Do Mice Have Bones?

Mice have bones because they're vertebrate animals. Even so, they can squeeze through the smallest holes without much effort.
Do Mice Have Bones?

Last update: 31 December, 2021

Small rodents are adorable creatures, but above all, they’re experts elusive. Watching them squeeze through the tiniest gaps will make you wonder if mice have bones or not, as their dexterity is unattainable for creatures like humans.

Despite what our eyes tell us, the answer to this question is yes. All rodents have a complex skeletal system. So how do they get that incredible flexibility? In this article, you have the answer to this and more questions, as you’ll find a complete review of the bone structure of mice. Keep reading!

What is a mouse?

What is commonly known as a mouse is actually a grouping of rodent mammals belonging to the genus Mus. The most well-known species of this taxon is the house mouse or Mus musculus, as it maintains a commensal relationship with humans in most cities and towns. Some representatives of the genus Apodemus are also considered common mice.

These rodents are small animals, as they don’t usually exceed 8 inches from the head to the tip of the tail. Their diet is omnivorous, although it’s usually based on seeds and vegetables for the most part. However, in urban areas, they don’t waste almost anything edible (including cockroaches, sweets, bread, and much more).

Mice usually live in burrows dug in the ground (with several exits) and only come out of them at night to feed. They usually don’t stray too far from their hole, as they might have to run for cover in case a predator appears. This is extremely common in the wild: They’re the favorite victims of many birds and mammals.

However, if they don’t make it home in time to get to safety after detecting a threat, mice can sneak into any nook and cranny, no matter how small. How do they do it? The following sections provide the answer.

A mouse nibbling on grass.

Do mice have bones?

Mice are vertebrate animals, which means they have a backbone and a bony structure that supports and shapes their bodies. The skeleton of mice is very similar to that of any other rodent: They have an elongated skull, a spine that extends almost all the way to the tail, and 4 limbs. Let’s take a look at it in parts:

  • Skull: In addition to protecting the brain, it’s the place where the sensory organs sit and connect directly to the brain through the nerve pathways. It also includes the highway of entry of food through the mouth, which is the beginning of the digestive system.
  • Spinal column: This is the shield of the spinal cord and from it, all the peripheral nerves radiate to the rest of the body.
  • Ribs: These bones create the rib cage by joining with the sternum so that they protect vital organs such as the heart and lungs. The intercostal muscles are involved in the breathing process, inflating the lungs along with the diaphragm.
  • Pelvis: This is the mechanical support for the hind legs of the mouse. It also protects the pelvic organs, such as the bladder and uterus.
  • Limbs: Because they’re assembled with the joints of the pelvis and scapulae, the forelegs and hind legs (along with the tail) allow the mouse to move.

How many bones does a mouse have?

The total number of bones a mouse has depends on the species, but the average is 200. The vertebral formula of mice is 7C-13T-4/6L. In other words, they have 7 cervical vertebrae, 13 thoracic vertebrae, 4-6 lumbar vertebrae, and a variable number of caudal vertebrae, as it depends on how long the tail of the specimen is.

Why do mice pass through impossible gaps?

As mentioned at the beginning, part of the success of the mouse’s survival depends on its speed in finding shelter. However, if we imagine someone of our species entering through the holes where they enter, the first thing that comes to mind is “I won’t fit”.

So, how do rodents do it? Do mice have flexible bones? Nothing could be further from the truth. The main reason they can achieve this feat is that their vertebrae are held together by ligaments that are more flexible than ours, as well as being spaced farther apart than a human’s (in proportion).

A young mouse can fit through an opening 7 millimeters in diameter, the equivalent of the thickness of a pencil.

Therefore, their spine bends much more easily than that of other animals, making the rodent’s body much more flexible. In addition, the subcutaneous space is another advantage when passing through narrow places, as the skin isn’t attached to the muscle.

Their intelligence also counts

These vertebrates are known for the great intelligence they possess. It’s not just about having a flexible spine, it’s about knowing where you can fit and where you can’t.

Mice instinctively know that their skull is the only bone in their body that they can’t bend, so it’s the ideal measure to fit through a hole. To measure the diameter of a passageway, they mainly use their whiskers, sensory organs that help them get a spatial representation of what’s right in front of them.

At the cortical level, the mouse’s vibrissae have a larger area of sensory activation than the legs and other areas of the head.

From there, the formula is simple: if the skull fits, so does the rest of the body. Once the head has passed through the hole, it’s only a matter of time before the mouse is able to squash itself flat enough to fit through it, thanks to the great flexibility of its spine.

The skeleton of a rat.

Did you have any idea that the bones of mice were so efficient? Without any doubt, these animals have developed a series of fascinating escape mechanisms to escape from their predators. If you’re interested in the subject, we encourage you to continue investigating the anatomy of these animals, because big surprises often come in small packages.

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