Frog Anatomy: Everything You Need To Know

I was against dissecting a frog to discover its anatomy when I was in high school! I still hate the sight of blood or guts, and I love frogs. Luckily, one of my friends wanted to become a Doctor and was super excited about cutting something open. You can bet that I jumped on the chance to be her frog dissection buddy. I still learned a lot without having to hurt a poor innocent frog.

That being said, this article contains everything there is to know about frog anatomy with non-graphic diagrams. If you are like me, find a friend who wants to go into the medical field and focus on my notes below. Then go out and save a few frogs in the wild after class to make up for the dissection.

We have many frog anatomy resources on this blog so click on the links in the article to learn more about different frog parts and their functions.

A Frog Anatomy Changes Greatly Through Metamorphosis

A frog’s anatomy goes through profound transformations via metamorphosis. Frogs are slightly similar to other amphibians like salamanders since they are cold-blooded, are born in water, and can live on land as adults. However, what differs frogs from other amphibians is the fact that they lose their tail in adulthood, thus the name “Anura,” which means “tailless” in Greek.

As a general rule, the frog life cycle consists of 4 main stages: Egg, Tadpole, Froglet, Adult Frog. The evolution through these stages is called metamorphosis and complete transformation can take up to 28 weeks depending on species and climate.

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Frogs have a wonderful and changing anatomy throughout their lifetime. Very few species on Earth have this ability. Frogs have been found as far back as 250M years ago. As of today, there are over 7,200 identified frog species worldwide. Most of them have similar internal anatomy, regardless of their size.

I know you probably have an adult frog on the dissection table so we will get to that in a few seconds. Let’s just quickly discuss the stages that the frog went through before becoming a high school science experiment.

Frog Egg Stage

The first stage of a frog’s life cycle is when they are an egg. Male and female Anura reproduce by amplexus (learn more in this article on our blog). Female Anura will lay their eggs in water, and the male Anura will fertilize them as they come out. Eggs are round, sticky dots that cluster (for frogs) or string together (for toads).

Frog Tadpole Stage

Tadpoles or Polliwogs are the aquatic larval stage of frogs that evolved from eggs after 3 to 25 days. They measure about 40-45mm and live in water. Tadpoles evolve for 14 to 16 weeks depending on the species and the climate in which they live.

Once frog eggs have hatched, they will turn into tadpoles. While still very small, they are extremely agile. Tadpoles have a tail to help them swim and gills to help them breathe while in the water. After a few weeks, tadpoles will start to sprout hind legs as they start to go through metamorphosis to become adult frogs.

Young Frog Stage (Froglet)

After the tadpole has sprouted front legs, they will start to migrate towards land and transform into froglets, or young frogs. During this life stage, young frogs grow larger, lose their tail and become adult frogs that can reproduce after 2 to 4 years depending on the species.

Learn more about the full frog life cycle in this article on our blog (it also contains up-close images of frog eggs and tadpoles).

External Anatomy of an Adult Frog

I much prefer to observe frogs in the Wild. But since you are going through what I did, having to dissect a poor frog for observational purposes, we have to be practical and get through this without getting sick. So ask your medical-bound friend to wait for a second and let you have a look at the frog’s external anatomy before you can no longer look at it anymore.

In most High Schools in Canada and the USA, Bullfrogs and Leopard Frogs are used for anatomical dissections. Bullfrogs are invasive in some places since they can grow very large and eat just about anything they can fit into their mouths including mice, bats, and birds. 

But poor Leopard Frogs are being overexploited for dissection and human consumption

I digress.

These are both aquatic frogs, but keep in mind that there are two other types of frogs you may have seen in the wild (CTNF).

Three Main Types of Frogs

Like I did in high school, you probably have an aquatic frog on the table. They are very common in North America and in Europe and are often used for dissections because they grow large enough to observe up close. But keep in mind that aquatic frogs are not the only kinds of frogs you can find in the wild. 

Generally, there are 3 main types of frogs that you can find in the wild, including Aquatic Frogs, Arboreal Frogs, and Terrestrial Frogs. Aquatic Frogs live in water, Arboreal Frogs live in trees and Terrestrial Frogs are generally Toads that live on land.

Learn more about different types of frogs in this article on our blog.

Frog Respiratory System: Frog’s Skin Helps Them Breathe & Drink  

Frog skin is thin, moist, delicate, slimy, permeable, and allows frogs to breathe, drink, and protect themselves. Frog skin can be used in pharmaceuticals for its antibiotic resistance fighting properties, and pain-killing properties. Some frogs secrete poison through their skin, and all toads have parotoid glands through which they can secrete toxins.

Frogs can breathe four different ways: through their lungs, nostrils, the lining of their mouth, and through their skin. Aquatic frogs prefer breathing through their skin while in water where they spend most of their time absorbing oxygen and stay hydrated.

We have a very detailed article on our blog about frog skin, check it out for more!

Frog Visual System: Frogs Have Complex Eyes

Frogs have three eyelids: one upper, one lower and a third eyelid called a nictitating membrane. The upper eyelid is used for blinking to keep eyes moist, the bottom eyelid does not move, and the nictitating membrane is used for swimming, camouflage, hibernation, and sleeping.

Here are some really cool frog eye facts:

  • Frog eyes bulge out to sit above the water
  • Frogs can see almost 360° around them
  • Frogs have three eyelids
  • Frogs use their eyes to swallow food
  • Frog pupils can be horizontal or vertical
  • Frogs can see in color at night

Frogs rely heavily on their vision to catch food and avoid predators. They pretty much spend the vast majority of their day making one of two decisions: Can I eat this? Will this eat me? Frogs need to make this life or death decision very quickly since they could be eaten if they do not move fast enough. 

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If they see a predator, frogs may employ one of their many self-defense mechanisms like urinating, camouflaging, or playing dead. Having an excellent vision is key to helping frogs make the right decisions at the right time.

Frog Auditory System: Frogs Hear Using Their Tympanum

Generally, frogs can hear thanks to their tympanic membrane that is situated on their heads behind their eyes. Frogs also pick up vibrations through their skin allowing them to interpret their environment. Some frogs can also hear with their lungs or mouth lining.

Behind the frog’s eyes, you can find the tympanum that frogs use to hear. Their “ears” are housed by tympanic cartilage, where a frog has other bones such as the stapes. This helps a frog hear and stay balanced.

Learn more about how frogs hear in this dedicated article on our blog.

Frogs Have Incredible Feet

Arboreal Frogs have padded toes on their feet that are made to stick to vegetation and allow them to climb. Aquatic Frogs have webbed feet and long powerful legs that make them excellent swimmers. And Terrestrial Frogs (like Toads) have finger-like toes made for digging.

Most high school frog dissections involve aquatic frogs, so you probably have a frog that has webbed feet. This webbing helps them be powerful swimmers since their feet can act like flippers that propel them in the water. Having webbed toes allows frogs to have more velocity and swim faster by pushing the water behind them with more force and volume.

You can learn more about frog feet depending on the type of frog in this article on our blog.

Internal Anatomy & Organs of Adult Frogs

Ok, so now is the time to hand the reins over to your lab partner who is annoyed you are taking forever to let them finally dive into their dissection. I never understood how people want to actually dissect anything, but we truly need people like that in society to save lives. So, let’s look at this from a positive perspective, thank goodness for your lab partner.

However, you need to take care of yourself in this situation, especially if you get sick easily. What I did was look away and just focus on the ugly diagrams our teacher gave us. But I tried to make you more interesting pictures to look at below, so you can still learn something without having to contribute to the massacre going on around you.

Frog Digestive System

A frog’s digestive system starts with their long, sticky tongues that they use to catch their prey. Inside their mouth, frogs also have small teeth, and a set of two larger teeth. These are not really used to chew since frogs swallow their prey alive and whole. Their teeth are used mostly to keep back their prey. Learn everything there is to know about frog teeth in this article on our blog.

After a frog has trapped its food in its tongue, it swallows it and pushes it down with its eyes. A frog will somewhat suck its eyes into its mouth to swallow the food.

The prey then travels to the stomach through the esophagus to break down and travel into the small intestine which will then further absorb nutrients. Frogs also have a large intestine.

Frogs also have a liver and pancreas to create the digestive enzymes needed to break down food and convert them into nutrients to feed their bodies.

At the end of a frog’s digestive system is the anus, which is the external portion of the cloaca. The external cloaca is used for excretion and reproduction. One question I know people are asking has to do with frog butts.

As a general rule, frogs do not have well-defined human-like buttcheeks since frogs do not sit on their rear ends at a 90° angle as humans do. Frogs generally have a pointed or rounded vent (or butt). However, some frogs do have what look like human-like buttcheeks.

Source: @Marron.chestnut777

You can learn more in the article about frog butts on our blog.

Frog Respiratory System

Frogs breathe utilizing four different respiratory methods, including the skin, lungs, nostrils, and lining of the mouth. The type of respiration used will vary depending on where the frog is located. Before metamorphosis into an adult frog, tadpoles breathe through their gills.

A frog’s skin is an important part of its respiratory system. For optimal respiration, a frog’s skin must stay moist and hydrated, which is why frogs never travel too far from a water source. If a frog’s skin dries up, it could have a much harder time breathing and drinking and will probably die.

Learn more about how frogs breathe in this dedicated article on our blog. 

Frog Reproductive System

As with most species, male and female frogs have different reproductive organs. Frogs reproduce externally by amplexus.

Female frogs have ovaries to create eggs and oviducts to transport the eggs to the cloaca. Male frogs have testes that produce sperm to exit through the cloaca to fertilize a female’s eggs as she lays them. 

Males also have a small thumb (known as the nuptial pad) to help them stay mounted on the females to efficiently fertilize the eggs.

Learn more about how frogs reproduce in this article on our blog.

Frog Musculoskeletal System

Frogs are vertebrates, meaning they have bones throughout their entire body. Their bones provide body structure, organ protection, and a basis for movement.

A frog has a flattened skull made of many small bones and some cartilage to protect its brain. The frog’s skull forms the structure and organization of other organ systems that start in the frog’s head, such as the digestive and olfactory systems.

Frogs have no neck, restricting their ability to turn their heads to look for food and check for predators so their eyes do most of the work thanks to 360° vision.

Inside a frog’s throat, you can find their vocal sac that they use when they croak, and their thyroid, trachea, and larynx, which are protected by cartilage. Only male frogs can croak.

Aquatic Frogs are known for their long hind legs that help them jump. They also have shorter front legs to help with balance. Their leg length had also adapted to help them swim in the water since they lost their tail as froglets. Aquatic Frogs also have webbing between their toes to help them swim more efficiently.

Learn more about how frogs move in this article on our blog.

Frog Circulatory System

At the center of every circulatory system is the heart, and the frog is no exception to this. A frog’s heart has three chambers to circulate blood around its body. 

A frog’s heart is different from humans’ because it is the only organ found in the coelom (chest cavity). Frogs are cold-blooded animals, but their blood is still used to oxygenate their body and transport nutrients throughout. 

Anatomical Differences Between Frogs and Toads

I had never seen an Aquatic Frog up close like that until it was time to dissect it. Thank goodness my lab partner let me only take notes during the dissection. But I had toads in our yard for years and was wondering what made this Aquatic Frog different from the ones in our backyard.

Here are some differences between Frogs and Toads:

FrogToad
EggsClustersStrings
TadpoleSlim BodyFat Body
SkinSmooth, MoistDry, Bumpy
Leg LengthLongShort

Learn more about the anatomical differences between frogs and toads in this article on our blog.

Precautions When Dissecting a Frog

Some teens love it, and others dread the day their biology teacher announces it’s time to dissect a frog. I was dreaded that day. Biology classes have used frog dissection to teach students to identify organs and learn about anatomy for many years, but let’s agree, this practice is more than outdated.

Thank goodness some schools have started to opt for digital dissections to conserve species and avoid traumatizing some students (like myself). I think dissections can be great for future medical students, but let’s be honest, not all of us want to or should become Doctors. But you may still have to go through dissecting a frog if your teacher is old school.

Here are some quick tips if you have to dissect a frog but don’t want to:

  • Chose an enthusiastic lab partner who wants to go into the medical field
  • Wear all protective gear, including goggles and gloves
  • Wash your hands with soap and water for at least 20 seconds before and after
  • Keep all your surfaces clean before, during, and after the dissection
  • Don’t chew gum, eat, or drink during the dissection
  • Try to focus on taking notes and making schemas
  • If you are uncomfortable or feel dizzy inform your partner or teacher

And if you can muster up the courage to talk to your teacher who should have retired ten years ago but can’t because they are underpaid, well, tell them you think this practice is more than outdated.

Good luck 🙂 

Sources

A Laboratory Guide to Frog Anatomy, by Eli C. Minkoff

AmphibiaWeb. 2021. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 26 May 2021.

Penn State, Biology Course, Frog Dissection