A body cavity is any space or compartment, or potential space, in an animal body. Cavities accommodate organs and other structures; cavities as potential spaces contain fluid. The two largest human body cavities are the ventral body cavity, and the dorsal body cavity. In the dorsal body cavity the brain and spinal cord are located. The membranes that surround the central nervous system organs (the brain and the spinal cord, in the cranial and spinal cavities) are the three meninges. The differently lined spaces contain different types of fluid. In the meninges for example the fluid is cerebrospinal fluid; in the abdominal cavity the fluid contained in the peritoneum is a serous fluid. In amniotes and some invertebrates the peritoneum lines their largest body cavity called the coelom. Mammals Mammalian embryos develop two body cavities: the intraembryonic coelom and the extraembryonic coelom (or chorionic cavity). The intraembryonic coelom is lined by somatic and splanchnic lateral plate mesoderm, while the extraembryonic coelom is lined by extraembryonic mesoderm. The intraembryonic coelom is the only cavity that persists in the mammal at term, which is why its name is often contracted to simply coelomic cavity. Subdividing the coelomic cavity into compartments, for example, the pericardial cavity / pericardium, where the heart develops, simplifies discussion of the anatomies of complex animals. Cavitation in the early embryo is the process of forming the blastocoel, the fluid-filled cavity defining the blastula stage in non-mammals, or the blastocyst in mammals. Human body cavities The dorsal (posterior) cavity and the ventral (anterior) cavity are the largest body compartments. The dorsal body cavity includes the cranial cavity, enclosed by the skull and contains the brain, and the spinal cavity, enclosed by the spine, and contains the spinal cord. The ventral body cavity includes the thoracic cavity, enclosed by the ribcage and contains the lungs and heart; and the abdominopelvic cavity. The abdominopelvic cavity can be divided into the abdominal cavity, enclosed by the ribcage and pelvis and contains the kidneys, ureters, stomach, intestines, liver, gallbladder, and pancreas; and the pelvic cavity, enclosed by the pelvis and contains bladder, anus and reproductive system. Ventral body cavity The ventral cavity has two main subdivisions: the thoracic cavity and the abdominopelvic cavity. The thoracic cavity is the more superior subdivision of the ventral cavity, and is enclosed by the rib cage. The thoracic cavity contains the lungs surrounded by the pleural cavity,