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Do Rats Have Bones? (How They Squeeze Under Doors)

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Yes, rats have bones. Rats are vertebrates with a skeletal system made up of bones connected by cartilage. Their bones are as stiff, yet rats can squeeze through holes or spaces smaller than their bodies.

The misconception that rats do not have bones springs from the fact that they can squeeze through holes smaller than themselves. 

Rat-proofing your home is difficult because of its skeletal structure.They can make their way to your house through the smallest openings.

In this article, you learn about rats’ bones, how many they have, and how they work.

Rat Bone Structure

Rats are vertebrates, meaning they have a spine to which all other bones are connected. This makes up the skeleton. The bones are strong and not cartilaginous, similar to other mammals. Their bones are connected to each other by joints and cartilage.

The skeleton of rats consists of bones connected to each other by joints and cartilage. 

Rats’ bones are divided into five sections:

  • Head bones
  • Spine bones, including tail bones
  • Ribs and sternum
  • Pelvic and shoulder bones
  • Limb bones

Head bones

Rat Head bones
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Rats have a series of bones[1] in their head:

BoneDescription
MandibleToothed bone that forms the lower jaw.
Maxillary boneIt is a toothed bone. Together with the premaxilla it forms the upper jaw.
Incisive bone It supports the upper incisive teeth.
Nasal boneRepresents the bones of the nose.
Frontal boneIt is a flat bone of the skull, located in the forehead region.
Zygomatic arch It has a role in protecting the eye and providing an articulation for the mandible.
OrbitIt has a role in protecting the eye.
ParietalIt is a flat bone, part of the upper part of the skull.
Tympanic bulla (Bulla tympanica)It helps to strengthen the sound, also favoring the communication between individuals.
Occipital condyle Together with the first cervical vertebra (atlas), it forms a hinge joint that allows flexion and extension of the head.

Spinal bones (Including Tail Bones)

Rat Spinal and Tail bones
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The spinal bones are called vertebrae. Rats have in total around 57 vertebrae.

There are five categories[2] of vertebrae:

  • Cervical (7 vertebrae)[3]
  • Thoracic (13 vertebrae)
  • Lumbar (6 vertebrae)[4]
  • Sacral (4 vertebrae)
  • Caudal (27-30 vertebrae that forms the tail)

Ribs and sternum

Rat Ribs and sternum
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Rats’ ribs are thin and curved bones that articulate with the sternum and spine. Together they form the rib cage.

The sternum is an elongated, flat bone with a crest on its surface.

Pelvic and shoulder bones

The pelvic bones contain the following segments:

IliumLarge flat back bone that articulates with the sacral vertebrae.
IschiumIt is found behind the ilium.
PubisVentral bone posterior to the ilium.

Together all three form the pelvic girdle. It connects the hind limbs to the trunk.

The shoulder bones consist of the following bones:

ClavicleIt is a long bone that articulates with the sternum and is located in the frontal ventral portion of the body.
Scapula (shoulder blade)It is a thin flat shoulder bone that articulates with the humerus.

Together they form the scapular girdle (pectoral girdle) and play a role in connecting the anterior limbs to the trunk.

Limb bones

Rat Limb bones
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Rats have four legs, also called limbs. They have two forelimbs and two hind limbs.

The forelimb skeleton consists of the following bones:

HumerusIt articulates with the scapula, radius, and ulna.
RadiusA long bone partially fused with the ulna. It is located between the humerus and the carpus.
UlnaA long bone partially fused with the radius. It is located between the humerus and the carpus.
Carpus (wrist)It consists of many short bones.
MetacarpusIt consists of several long bones and connects the carpus to the first phalanges.
PhalangesBones that form the skeleton of the fingers. Rats have four fingers on each front paw, lacking the opposable thumbs.

The hind limb skeleton consists of the following bones:

FemurIt is a long bone that articulates with the patella. It is the longest bone in the body.
TibiaA long bone partially fused with the fibula that is located between the femur and tarsus.
FibulaA long bone partially fused with the tibia. It is located between the femur and tarsus.
PatellaIt is a small triangular and flat bone. Together with the tibiofemoral joint, it forms the knee.
Tarsus (ankle)It consists of many short bones.
MetatarsusIt consists of several long bones and connects the tarsus to the first phalanges of the foot.
PhalangesBones that form the skeleton of the fingers. Rats have five toes on each front foot.[5]

How Many Bones Does a Rat Have?

Rats have about 223 bones. The number of bones depends on the species and the length of their tail. These animals are vertebrates that have a body made up of bones and muscles.

Rats can fit through narrow spaces, not because they have no bones but because they have a long, cylindrical, and flexible skeleton.

How Many Bones Does a Rat Have
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Do Rats Have Bones in Their Tails?

Yes, rats have bones in their tails. The number of bones varies depending on the species. The tail bones are caudal vertebrae. Common rats have 27-30 tail bones (Rattus rattus and Rattus norvegicus).

The tail is not covered with scales (as many people think) but with fine hairs. Rats’ tail serves several purposes[6] and roles:

  • Thermoregulation
  • Maintaining balance
  • Thwarting predators

Do Rats Have Pneumatic Bones?

No, rats do not have pneumatic bones. The bones of rats are full of marrow. Pneumatic bones are bones full of air. These are important for bird respiration.

How Big Can Rats Get?

The size of a rat depends on several factors. Common rats can reach a length of 10 inches (25 cm) without the tail and a body weight of 1.5 lbs. (700 g). Their tail is as long as their body, or slightly shorter. Black rats have a shorter tail compared to brown rats.

Many factors determine how big rats grow in adulthood:

  • The species
  • Sex (males are larger than females)
  • Age (pups are smaller than adults)

The smallest rat (Osgood’s rat from Vietnam) is about five inches long, while the largest one (Sumatran Bamboo Rat from China and Sumatra) can grow up to 20 inches long without the tail.

Common rats, which are often found in homes or on the streets, reach about 10 inches long and 1.5 lbs body weight when fully grown. 

Although rats seem big to sneak through small holes, they have a long, flexible skeleton that allows them to do so.

Related article: How Big Do Rats Get?

How Big Can Rats Get

How Can Rats Fit Into Small Spaces?

Rats can fit into small spaces because they have tilted collarbones. This allows them to squeeze into small holes or narrow spaces. They have a long, narrow body and strong legs that also help push them through small openings.

This ability is not seen in all rats. Fat ones or larger species are not able to pass through the same small holes that smaller rats can get through.

Obese rats tend to concentrate the fat around the abdomen, which leads to an inability to pass through small holes and narrow spaces.

How Small of a Hole Can a Rat Get Through?

Rats can pass through holes the size of a quarter, or about 0.96 inches in diameter. Only small rats can squeeze through holes this small. Obese rats can not pass through 1-inch holes no matter how hard they try.

If you want to buy to protect your house and garden from rats, consider the size of the wire mesh you’re going to buy.

Wire nets with 1×1 inch holes are too large to keep rats away. The most suitable are those with holes of 1 by ½ inch or even ½ by ½ inch.

How Small of a Hole Can a Rat Get Through

Can Rats Squeeze Under Doors?

Small or juvenile rats can squeeze under doors, but not adult rats. For a rat to squeeze under a door, the size of the rat and the size of the space under the door have to be taken into account. If the space under the door is at least the size of a quarter, small rats can squeeze under without problems.

Rats squeeze under doors the same way they pass through small holes and cracks.

Rat Bones Compared to Humans

The bones of rats are similar to those of humans. They have a skeleton consisting of the head, spine, and limbs, with bones full of bone marrow.

Here are the differences between the bones of rats and humans:

  • Rats have 223 bones, with 17 more than humans, which have 206 bones.
  • Rats only have four fingers, not having the opposable one.
  • They have 20-30 caudal vertebrae, while people have much fewer.
About Iulia Mihai (DVM)

Dr. Iulia is a certified veterinarian with more than 10 years of experience in the field. With extensive knowledge of diet, care, and medication, she helps Misfit Animals provide readers with accurate knowledge on technical topics.

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