Hymen

The hymen (also called the maidenhead) is a thin fold of membranous connective tissue which "encompasses (surrounds) the lumen of the vagina". It surrounds and partially covers the opening of the vagina all around the edges, or sometimes completely blocks it (called a imperforate hymen) until it is fixed. It is close to behind or deeper inside the labia minora. 

The hymen has no known use. People used to believe that the hymen always tears after having sexual intercourse for the first time, and that you could tell if a woman was a virgin by looking at her hymen and seeing if it was torn. However, it turns out that it is impossible to tell if someone is a virgin by looking at their hymen. Studies have confirmed that all girls are born with hymens.

 Types 
There are several different types of hymen. In about 1 in 2,000 females, the hymen does not develop at all. The hymen may also not have a hole in it; this is called an "imperforate hymen". In this case a hole will need to be surgically cut into it to allow menstrual fluid (period blood) or other secretions out.Chang, Lisbeth and Muram, David. (2002) "Pediatric & Adolescent Gynecology" in DeCherney, Alan H. and Nathan, Lauren. Current Obstetric & Gynecological Diagnosis & Treatment, 9th edition, McGraw-Hill, 598-602. Without this surgery, the patient might feel discomfort, pain, or be more prone to vagina infections. 

Other types of hymen are:

 crescent-shaped
 folding in on itself
 has one or more bands going across the opening
 has several holes

 What might damage the hymen 
When a girl reaches puberty, the hymen becomes stretchy. The hymen may be damaged by girls fall directly onto sharp objects .Emans, S. Jean. "Physical Examination of the Child and Adolescent" (2000) in Evaluation of the Sexually Abused Child: A Medical Textbook and Photographic Atlas, Second edition, Oxford University Press. 64-5 

Sexual intercourse is an easy way to damage the hymen along with horseback riding and biking. A woman's hymen can also break while playing some sports.

 Hymens in other animals 
These animals all have a hymen:
 Squirrels
 Gazelles
 Frogs
 Bats
 Cats
 Chimpanzees Dogs
 Elephants
 Llamas
 Guinea pigs
 Horses
 Bears Zebras
 Lemurs
 Manatees
 Rats
 Seals
There are many more animals which have hymens, but not all are listed here.

 The stages of growth 
When a fetus is developing, there is no vaginal opening. The hymen comes from the skin covering the vagina at that time.1918 Gray's Anatomy

In young babies, the hymen is thick and pink. This is because the mother is giving the baby hormones through breast feeding which keeps it thick. In adolescent girls, the hymen becomes thin, smooth and delicate because she has stopped taking in hormones. The hymen becomes very sensitive and can easily cause pain if touched. From puberty, the hymen gets thicker again and becomes pale pink. This is because of the hormone estrogen.

 References 

 Other websites 

The Female Hymen and its Significance
Hymen gallery  - Pictures of hymens
The Hymen Revealed  - by The-Clitoris.com

Category:Anatomy of the female reproductive system