Snake Anatomy 101: What Makes a Snake, Inside and Out

There's a lot more inside of snakes than a forked tongue and a bunch of bones. Dorling Kindersley / Getty Images/Dorling Kindersley

Unlike most other animals, snakes do not have limbs to help them get from one place to another. Instead, they slither — but there's a little more to snake anatomy than how they move. Finely tuned for survival, snakes have specialized anatomy that let them thrive in diverse environments.

External Anatomy of a Snake

First things first, let’s talk about what you can see on the outside of a snake. These external features help snakes navigate their environment, find prey and defend themselves.

Forked Tongue

One of the most recognizable features of snakes is their forked tongue. Snakes flick this unique organ in and out of their mouths, using it to collect particles from the air.

The forked shape helps them pick up chemical signals from both sides of their environment, which they process using a special organ called the Jacobson’s organ (located on the roof of their mouth). This allows them to detect the "scent" of their prey items, as well as navigate and find mates.

Heat-sensing Organs

Found on the faces of species like pit vipers, these organs let snakes detect warm-blooded prey, even in the dark. They can "see" like a thermal camera.

Spectacles

These transparent scales, or spectacles, cover snakes' eyes.

Nostrils

Located on their heads, nostrils help snakes breathe and detect odors.

Scales

Snakes have a few types of scales, including:

Dorsal scales: Located on the backs of snakes and used for protection and movement
Ventral scales: Larger, specialized scales on the underside of the snake
Subcaudal scales: Found on the underside of the tail

Cloaca

An external opening located near the base of the tail, the cloaca is for excretion and reproduction.

Tail

This is the portion of the snake's body after the cloaca, often tapering to a point. Some snakes, like rattlesnakes, have specialized features like a rattle at the tip.

Teeth or Fangs

Nonvenomous snakes have small, recurved teeth, while most venomous snakes have grooved or hollow fangs for delivering venom.

Nuchal Ridge

The ridge along the back of the head or neck that is prominent in some species.

Internal Anatomy of a Snake

Unlike most animals, snakes have elongated bodies, with their organs stretched out.

Glottis: Located at the front of the mouth, this allows the snake to breathe even while swallowing large prey. The glottis can move to the side to keep the airway open.
Lungs: Instead of having two equally sized lungs, a snake's right lung is the primary lung, while the left lung is either much smaller or absent altogether. This unique feature allows snakes to have more room in their bodies for large prey items.
Digestive system: After swallowing prey whole, food travels through the esophagus and into the stomach, where digestion begins. The small intestine absorbs the nutrients before it passes through to the large intestine, which processes waste.
Jaws: Snakes have a highly flexible lower jaw that doesn't fuse like ours. This flexibility allows them to "unhinge" their jaws, stretching their mouths wide enough to swallow prey much larger than their head. Each side of the lower jaw moves independently, helping the snake work its prey down its throat in a kind of "walking" motion.
Skull: Snakes have highly flexible skulls that allow them to swallow prey much larger than their heads.
Vertebrae: Snakes have a large number of vertebrae (up to 400 in some species), which provide support and flexibility.
Ribs: Snakes have ribs extending from nearly every vertebra, providing protection and aiding in movement.
Muscular system: Snakes have powerful muscles that run along their bodies, helping them slither, constrict prey and swallow food. The muscles are arranged in segments corresponding to the vertebrae and ribs.
Brain: Snakes have a small brain compared to their body size, but it can control essential functions like movement, feeding and sensory processing.
Spinal cord: Running the length of the body, the spinal cord transmits signals between the brain and body, coordinating movement and reflexes.
Nerves: Nerves branch out from the spinal cord to control various muscles and organs.
Heart: The snake's heart is closer to the head, around one-quarter down the length of its body. It has three chambers: two atria and one ventricle.
Blood vessels: The snake's circulatory system works efficiently with its long body, supplying blood to the muscles and organs as necessary.
Kidneys: Snakes have two kidneys, which filter waste from the blood. Unlike mammals, snakes have elongated kidneys, positioned one behind the other along the body.
Ureters: These tubes carry waste from the kidneys to the cloaca.
Reproductive system: Male snakes have hemipenes, paired reproductive organs that are inside the base of the tail. Female snakes have paired ovaries that produce eggs and oviducts through which the eggs travel.
Jacobson's organ (vomeronasal organ): Located on the roof of the mouth, this organ detects chemical signals in the environment. The forked tongue gathers particles and delivers them to this organ.
Lymphatic system: Snakes have a lymphatic system similar to other vertebrates, which helps in immune response and fluid balance.

What Distinguishes Snakes From Other Reptiles?

One of the most obvious differences between snakes and other reptiles is their lack of legs. Snakes use their muscles and scales to slither through their environment. This lack of legs also contributes to their elongated shape and specialized anatomy.

Snakes also do not have external ears. While many reptiles have external ears that help them hear sound waves, snakes only have an internal ear, which picks up vibrations from the ground. This ability allows them to "hear" in a completely different way from other reptiles, relying on their jawbones to detect movement and vibrations.

Another key difference lies in their feeding habits. Many reptiles, like lizards, bite off chunks of food or chew, but snakes swallow their prey whole. This is where the flexibility of their lower jaws comes in handy, allowing them to ingest prey much larger than their heads. The specialized set of teeth in their upper jaw grips prey as they work it down their throat.

And finally, many species of snakes can thrive in specific environments. For example, the hognose snake uses its uniquely shaped nose to burrow into loose soil, while other snakes have evolved labial pits to sense heat. These adaptations, along with the flexible anatomy of their jaws and organs, make snakes uniquely equipped for survival compared to their reptilian cousins.

We created this article in conjunction with AI technology, then made sure it was edited and fact-checked by a HowStuffWorks editor.