Re: comparing the skeleton of frog and human why do frogs have long pelvis bone

The pelvis of vertebrates that are tetrapod is designed to carry the larger of 
the animal’s limbs. If you are studying this at University, Benisa, then it is 
important to look at the overall life of humans and frogs. Frogs use their front 
legs a little like humans because they are not the main propulsive unit. But 
the hind limbs in both are highly modified for two specialised movements. 
While the human is truly bipedal and the pelvis has to support a huge mass 
of skull, back and viscera, the frog has its swimming and land locomotion 
directed from the pelvic bones and its attached muscles.
Land animals possess an ilium at the back of the pelvis which is the
 weight-bearing area of the frog’s back end. The pubic area of the pelvis
 meets with the ischium and the ilium at the femur bone’s articulation (called 
the acetabulum). Now this ilium is very special in frogs. While the leg bone 
articulates with one part of the pelvis, the long ilia on both sides stretch to
the vertebrae that the frog has on its sacrum. It’s very hard to imagine the 
shape of this unique pelvis. so  think of it as a sycamore or ash
fruit(helicopter), with the long, strong ilium forming a long lever from the
disc of the main pelvis. So when the frog jumps, the force transmits to the
backbone as it is propelled forward. The lever can move through 90o where 
the end of the ilia connects with the vertebrae. 
	So the skeletal and muscular adaptations of the frog are highly 
significant for its locomotion, with even the ulna and radius fused to give the 
animal more strength. It is only the long strong ilium of the pelvis which is 
highly modified so that it can reach the sacral vertebra on each side and give 
leverage for the cruralis and other muscles when they provide the motive 
force of the leap. I hope your answer was implicit in the question, but I hope 
the complications of our Amphibian friend’s anatomy aren’t too confusing.
	Hopefully this diagram will help to show the frog's whole anatomy:
 http://www.colszoo.org/animalareas/reptiles/frogfact.html		
  
  
and this one will show the pelvis perfectly!   ------

 http://froggy.lbl.gov/images/whole.frog/label1.jpg