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Human Fetus Four Months Old
The fetal heartbeat may now be audible through an instrument called a doppler. The fingers and toes are well-defined. Eyelids, eyebrows, eyelashes, nails and hair are formed. Teeth and bones become denser. The fetus can even suck his or her thumb, yawn, stretch and make faces. The nervous system is starting to function. The reproductive organs and genitalia are now fully developed. By the end of the fourth month, the fetus is about 6 inches long and weighs about 4 ounces.
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