Frogs have three-chambered heart.
Their skull is flat, except for an expanded area that encases the small brain. Only nine vertebrae make up the frog's backbone, or vertebral column. The human backbone has 24 vertebrae. The frog has no ribs.
Frogs use their skin and lungs for breathing (human use only lungs).
Frogs have teeth only on upper jaw.
Both liquid and solid waste material leave the body by way of the cloaca and the cloacal vent.
Only 10 cranial nerves originate in the frog's brain. Man has 12. Similarly, the frog has only 10 pairs of spinal nerves. Man has 30 pairs.
The eye is crude. Its fixed lens cannot change its focus. Poorly developed eyelids do not move. To close its eye, the frog draws the organ into its socket. A third eyelid, or nictitating membrane, may be drawn over the pulled-in eyeball.
There is no external ear. Both eardrums, or tympanic membranes, are exposed. There is only one bone in the frog's middle ear. The human middle ear contains three bones (ossicles). As in man, semicircular canals help to maintain body balance.