Generally, frogs are found in near waters and damp places on the land areas.
Rana is the common frog genus found in the world.
These animals can live in water or near water because of the following:
- To keep their skin moist for the cutaneous respiration
- To be able to quickly jump and slip into the water for escaping their enemies.
Frog External Anatomy
Following are the main external features of the frogs
Shape and Size
- The body of the frog is somewhat spindle-shaped, rounded posteriorly, and pointed anteriorly.
- In some cases, the body is slightly flattened dorsoventrally and streamlined to swim through the water areas.
- Commonly, the body is divisible into the head, trunk, and limbs with no neck and tail.
- The size of a general frog is approximately 12 to 18 cm in length and 5 to 8 cm in width.
- The frog has a tail at birth but it disappears as the frog grows by metamorphosis.
Skin and Color
- In general, the skin of the frog is thin, slimy, and moist for the application of cutaneous respiration.
- The skin is ill-fitted to the body of the frog, which remains like loose skin layers.
- The back part of the frog skin has dorsolateral folds and thickenings, called dermal plicae.
- It is seen generally, that the color of the frog’s skin is mainly green with black and yellow spots over it.
- In some cases, brown spots are also found in the central part.
- A light yellow mid-dorsal line is seen on the body of the frog which runs from the tip to the snout to the cloacal opening at the back of the body.
- Change in color of the skin is also seen in frogs due to the expansion of melanophores pigment.
Head
- The head of the frog is somewhat demarcated clearly from the trunk region.
- The region is a flat, and rough triangle in outline and with a blunt anterior snout that terminates in a wide transverse mouth.
- Two small openings are found on the head region which lies dorsally above the mouth tip of the snout and also serves in respiration.
- In the head region, the two protruding eyes are situated dorsolaterally on the top.
- When the eyes are pressed downwards, they make an imminent presence on the buccal cavity.
- Each eye has a thick and pigmented immovable lower eyelid.
- From this place, arises a thin, semi-transparent eyelid called a nictating membrane.
- This membrane covers the eye and protects during swimming and it keeps the eye moist all the time.
- Behind each of the eyes, there is a presence of a pigmented circular patch of skin called the eardrum or tympanum.
- This is responsible for collecting the sound waves.
Trunk
- In frogs, the head is broadly joined with a flat ovoid trunk with the body.
- Its back part is raised in the middle region in a characteristic sacral prominence of the hump.
- This hump is especially conspicuous when the frog starts to squat.
- The trunk is the region that encases the lungs, heart, digestive tract, liver, genitals, and kidneys.
- At the posterior end of the frog’s trunk, there is a small aperture called the cloacal aperture.
- This aperture is the vent that facilitates the discharge of fecal, and urinary wastes as well as the reproductive material like the sperms and ova.
Limbs
- The trunk of the frog laterally has two pairs of limbs.
- Here, the short limbs arise from the anterior part of the trunk, from just behind the head.
Each of the forelimbs has the
- The upper arm called Brachium
- Forearm called Antebrachium
- Wrist called Carpus
- Hand called Manus
The hand or manus bears 4 digits (fingers) without webbing.
Of these 4 digits, the thumb and pollex are vestigial in origin.
In the case of a male frog, the base of the first finger is thickened, which forms the nuptial pad in breeding seasons that helps in clasping the female amplexus.
The hind limbs are powerful and arise from the trunk region.
Each of the hind limbs consists of:
- the thigh
- Shank called crus
- Ankle called tarsus
- Large foot called pes
These hind limbs support swimming and walking on damp lands.
Sexual Dimorphism
Sexual dimorphism is strongly seen in the frog population.
Several imminent identifying features help in distinguishing male and female frogs, which are as follows:
- The males are smaller than the females and have darker shades than the males.
- Male frogs are slimmer, whereas, female frogs are stouter when they carry eggs.
- The male frogs croak louder, while the female frogs lack the eardrum present in males.
- The male frogs have swollen copulatory and nuptial pads on the inner fingers which are lacking in female frogs.
