In vertebrates such as mammals the abdomen (belly) constitutes the part of the body between the thorax (chest) and pelvis. The region enclosed by the abdomen is termed the abdominal cavity. In arthropods it is the most distal section of the body which lies behind the thorax or cephalothorax.

Abdominal organs
Digestive tract: Stomach, small intestine, large intestine with cecum and appendix
Accessory organs of the digestive tract: Liver, gallbladder and pancreas
Urinary system: Kidneys and ureters
Other organs: Spleen
Abdominal organs can be highly specialized in some animals. For example the stomach of ruminants (a suborder of mammals) is divided into four chambers - rumen, reticulum, omasum and abomasum.

The human abdomen (from the Latin word meaning "belly") is the part of the body between the pelvis and the thorax. Anatomically, the abdomen stretches from the thorax at the thoracic diaphragm to the pelvis at the pelvic brim. The pelvic brim stretches from the lumbosacral angle (the intervertebral disk between L5 and S1) to the pubic symphysis and is the edge of the pelvic inlet. The space above this inlet and under the thoracic diaphragm is termed the abdominal cavity. The boundary of the abdominal cavity is the abdominal wall in the front and the peritoneal surface at the rear.

Functionally, the human abdomen is where most of the alimentary tract is placed and so most of the absorption and digestion of food occurs here. The alimentary tract in the abdomen consists of the lower esophagus, the stomach, the duodenum, the jejunum, ileum, the cecum and the appendix, the ascending, transverse and descending colons, the sigmoid colon and the rectum. Other vital organs inside the abdomen include the liver, the kidneys, the pancreas and the spleen.

The abdominal wall is split into the posterior (back), lateral (sides) and anterior (front) walls.

Gymnasiums (i.e., places for gymnastics) in Germany were an outgrowth of the Turnplatz, an outdoor area for gymnastics, promoted by German educator Friedrich Jahn and the Turners, a nineteenth-century political and gymnastic movement. The first indoor gymnasium in Germany was probably the one built in Hesse in 1852 by Adolph Spiess, an enthusiast for boys' and girls' gymnastics in the schools. In the United States, the Turner movement thrived in the nineteenth and early twentieth centuries. The first Turners group was formed in Cincinnati in 1848. The Turners built gymnasiums in several cities like Cincinnati and St. Louis which had large German American populations. These gyms were utilized by adults and youth. For example, a young Lou Gehrig would frequent the Turner gym in New York City with his father.

Gymnasiums in the United States predate the Turner movement. A public gymnasium movement sprung up in the 1820s and 1830s but was eclipsed by the growth of school, college, and the Young Men's Christian Association (YMCA) gymnasiums. The first college gymnasium probably was the one built at Harvard University in 1820. Although privately owned, it was maintained for the use of the students. Like most of the gymnasiums of the period, it was equipped with gymnastic apparatus. The United States Military Academy at West Point built a gym during the same era. A few other American colleges built gyms by the 1850s. Harvard opened a new brick gymnasium in 1860 with two bowling alleys and dressing rooms in addition to the gymnastic facility.

YMCA first organized in Boston 1851. Ten years later there were some two hundred YMCAs across the country, most of which provided gymnasiums for exercise and games and social interaction.

The 1920s was a decade of prosperity that witnessed the building of large numbers of public high schools with gymnasiums. Over the course of the twentieth century, gymnasiums have been reconceptualized to accommodate the popular team and individual games and sports that have supplanted gymnastics in the school curriculum.

Today, having a gymnasium is the norm for virtually all American colleges and high schools, as well almost all middle and many elementary schools. These facilities are utilized for physical education, intramural sports and for interscholastic athletics.

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Gimnasios (es decir, los lugares de la gimnasia) en Alemania fueron un resultado de la Turnplatz, un área al aire libre para la gimnasia, promovido por el educador alemán Friedrich Jahn y la Turners, un político del siglo XIX y el movimiento de gimnasia. La primera cubierta gimnasio en Alemania era probablemente el construido en Hesse en 1852 por Adolph Spiess, un entusiasta de los niños y las niñas de gimnasia en las escuelas. En los Estados Unidos, el movimiento Turner prosperó en el siglo XIX y principios del siglo XX. Turners El primer grupo se formó en Cincinnati en 1848. El Turners gimnasios construidos en varias ciudades como Cincinnati y San Luis que había grandes poblaciones de América. Estos gimnasios fueron utilizados por los adultos y los jóvenes. Por ejemplo, un joven de Lou Gehrig frecuente que la Turner gimnasio en la ciudad de Nueva York con su padre. Gimnasios en los Estados Unidos son anteriores a la circulación Turner. Un público gimnasio movimiento surgido en la década de 1820 y 1830, pero fue eclipsado por el crecimiento de la escuela, la universidad, y de la Young Men's Christian Association (YMCA) gimnasios. El primer colegio gimnasio probablemente fue el construido en la Universidad de Harvard en 1820. Aunque de propiedad privada, que se mantuvo para el uso de los estudiantes. Al igual que la mayoría de los gimnasios de la época, que estaba equipado con aparatos de gimnasia. Los Estados Unidos en la Academia Militar de West Point construyó un gimnasio durante la misma época. Algunos otros colegios de América construido gimnasios por la década de 1850. Harvard ladrillo abierto un nuevo gimnasio en el año 1860 con dos bolera y vestuarios, además de la instalación de gimnasia. YMCA primero organizado en Boston 1851. Diez años más tarde hay más de dos centenares de YMCA en todo el país, la mayoría de los cuales siempre gimnasios para hacer ejercicio y juegos y la interacción social. El decenio de 1920 fue una década de prosperidad que ha sido testigo de la construcción de un gran número de escuelas secundarias públicas con gimnasios. En el transcurso del siglo XX, gimnasios han sido reconceptualized para acomodar el equipo y los populares juegos y deportes que han suplantado a la gimnasia en el programa de estudios. Hoy en día, tener un gimnasio es la norma para prácticamente todos los americanos a las escuelas secundarias y universidades, así como casi todos los medios y muchos de los colegios. Estas instalaciones son utilizadas para la educación física, el deporte y intramuros para interscholastic atletismo.