Parts of a Frog's Muscular System

By Cindy Quarters

Frogs are often dissected in biology classes to teach students firsthand about anatomy. Though frogs and humans have many similar structures, such as heart, lungs and musculature, they also have many differences, especially when it comes to the way their muscles function. Not only do frogs and humans move differently, they even breathe differently, and their muscles reflect this.

General Structure

Both humans and frogs have an internal skeleton that protects the internal organs. The muscles attach to the skeletal bones and allow movement. Differences between human and frog skeletons and muscles relate to how both function.

Skeletal Structure

The forelimbs of frogs and the arms of humans both consist of two larger sections with a joint in between. Both have a single upper bone, the humerus, but humans have two bones in their lower arms, the radius and the ulna. Frogs have only one, the radio-ulna.

Their hind legs are designed for jumping, consisting of an upper bone, the femur, which is the same as in humans, but a single “shin bone” known as the tibiofibula, where humans have two bones, the tibia and the fibula. These fused bones are much stronger and more suited to jumping than the bones humans have. Frogs also have an extra joint in their lower legs, giving them significantly more flexibility and potential power than humans.

Another difference between frogs and humans is the number of vertebrae. While humans have 24 vertebrae, ideal for standing upright and walking about, frogs have only nine. Fewer vertebrae means that the frog’s backbone is less flexible than a human’s. This means that it stays straight when the frog jumps, so the frog has more power and is less prone to injury.

Along with more compact backbones, frogs have no ribs to get in the way of jumping. This also means that they have less protection for their vital organs, plus they breathe differently than humans.

Muscle Structure

Frogs and humans both use striated, or skeletal, muscles for movement. The muscles in both species are typically connected to bone by aponeuroses or tendons. Movement is achieved when the skeletal muscles contract or relax. This type of muscle use is voluntary, which means that the brain of the person or frog making the movement controls what happens.

Many of the muscle structures of a frog are similar in nature to those of a human. Humans and frogs both use structures such as the gluteus, femoris and the gastrocnemius muscles to aid in movement. Both also have the pectorals and the deltoids in the chest or arm/front leg area. The difference is in the relative power of each of these muscle groups. A frog’s rear leg muscles are comparatively larger and stronger, to give it jumping and swimming power.

What Frogs Lack

One notable difference between a frog’s muscular system and a human’s is the frog’s lack of a diaphragm. This muscle is vital in humans, as it separates the upper portion of the body cavity from the lower and provides the power that works the lungs. Without a diaphragm, humans cannot breathe. Humans also use their ribs and chest muscles in breathing. Since frogs lack ribs those aren’t involved, and although they have chest muscles, these also have no part in respiration. Instead, a frog either gets air by opening its mouth and allowing air to flow in or by taking air into its mouth and then forcing air down into its lungs by lifting the mouth floor.