Summary of the Anatomy of the Frog
As in other higher vertebrates, the frog body may be divided into a head, a short neck, and a trunk. The flat head contains the brain, mouth, eyes, ears, and nose. A short, almost rigid neck permits only limited head movement. The stubby trunk forms walls for a single body cavity, the coelom (Anatomy of the Frog).
All the frog's internal organs--including the heart, the lungs, and all organs of digestion--are held in this single hollow space (Anatomy of the Frog).
The Skeleton and Muscles
The frog's body is supported and protected by a bony framework called the skeleton. The skull is flat, except for an expanded area that encases the small brain. ...view middle of the document...
Skeleton-moving muscles are made of skeletal, or "striated," muscle. Internal organs contain smooth muscle tissue.
There are two upper chambers of the heart, the right atrium and the left atrium. The frog heart, however, has only one lower chamber, a single ventricle. In man, the lower heart chamber is divided into two compartments, the right ventricle and the left ventricle (Anatomy of the Frog).
Oxygen-laden blood and oxygen-poor blood containing waste gases are present together in the frog ventricle at all times. The oxygen-laden and oxygen-poor bloods, however, do not mix. Such mixing is prevented by a unique arrangement of the frog's heart. Instead of "perching" on top of the ventricle, the right atrium dips downward into the ventricle. This causes oxygen-poor blood entering the right atrium to pass all the way down to the bottom of the ventricle (Anatomy of the Frog).
Meanwhile, oxygen-laden blood is received by the left atrium and enters the same single ventricle. The pool of oxygen-poor blood at the bottom of the ventricle holds up the oxygen-laden blood and prevents it from sinking to the bottom. When the oxygen-poor blood flows from the ventricle into vessels leading to the lungs, the oxygen-laden blood tries to "follow" it. The lung vessels, however, are filled with oxygen-poor blood, blocking the oxygen-laden blood and forcing oxygen-laden blood to detour into the arteries. These carry the oxygen-laden blood to the tissues. Frog blood has both a solid and a liquid portion. The liquid plasma carries solid elements such as red blood cells and white blood cells (Anatomy of the Frog).
The Skin and Respiratory System
The frog is covered by a soft, thin, moist skin composed of two layers, an outer epidermis and an inner dermis. The skin does not merely protect the frog but helps in respiration (Anatomy of the Frog).
An extensive network of blood vessels runs throughout the frog's skin. Oxygen can pass through the membranous skin, thereby entering directly into the blood. When a frog submerges beneath the water, all its respiration takes place through the skin. Oxygen is obtained directly from the water (Anatomy of the Frog).
The frog does not breathe through its skin alone. Adult frogs have paired simple, saclike lungs. The mechanism of breathing, however, is different in the frog from that in man. In humans breathing is aided by the ribs, the diaphragm, and the chest muscles. The frog has no ribs or diaphragm, and its chest muscles are not involved in breathing (Anatomy of the Frog).
A frog may breathe by simply opening its mouth and letting air flow into the windpipe. However, it may also breathe with its mouth closed. The floor of the mouth is...