Frog locomotion
PHOTO: AFP
Though frogs have legs, they always jump and do not walk. Why?
MASTER ABISHEKH
Thiruvananthapuram.
Frogs belong to the class "Amphibians". They are divided into three orders:
Apoda - These do not have limbs.
Urodela - These have limbs equal in size.
Anura - These have short fore limbs and long hind limbs.
Frogs are generally recognized as exceptional jumpers. There are tremendous differences between species in jumping capabilities. But within a species, jumping distance increases with increasing size, but relative jumping distance decreases.
While frog species can use a variety of locomotive modes (running, walking, gliding, swimming and climbing), more are either proficient at jumping or descended from ancestors who were with much of the musculo-skeletal morphology modified for this purpose. The tibia, fibula and tarsals have been fused into a single strong bone and have radius and ulna in the fore limbs.
The meta tarsals have become elongated to add to the leg length and allow the frog to push against the ground for longer during a jump. The ilium whichhas elongated and formed a mobile joint with the sacrum which in specialist jumpers such as Ranids or Hylids, functions as an additional limb joint to further power the leaps.
This elongation of the limbs results in the frog being able to apply force to the ground for longer during a jump which in turn results in a longer faster jump. The muscular system has been similarly modified.
The hind limbs of the ancestors of frogs presumably contained pairs of muscles which would act in opposition as seen in most other limbed animals. However, in modern frogs almost all muscles have been modified to contribute to the action of jumping, with only a few small muscles remaining to bring the limb back to the starting position and maintain posture.
M. RAMULU
Associate Professor
Dept. of Zoology
Janavignana Vedika
Warangal, Andhra.Pradesh
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