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It is composed of 270 bones at the time of birth, [2] but later decreases to 206: 80 bones in the axial skeleton and 126 bones in the appendicular skeleton. 172 of 206 bones are part of a pair and the remaining 34 are unpaired. [3] Many small accessory bones, such as sesamoid bones, are not included in this.
The abdominal cavity is a large body cavity in humans [1] and many other animals that contain organs.It is a part of the abdominopelvic cavity. [2] It is located below the thoracic cavity, and above the pelvic cavity.
The lungs, heart, stomach, and intestines, for example, can expand and contract without distorting other tissues or disrupting the activity of nearby organs. [2] The ventral cavity includes the thoracic and abdominopelvic cavities and their subdivisions. The dorsal cavity includes the cranial and spinal cavities. [2]
The axial skeleton (80 bones) is formed by the vertebral column (32–34 bones; the number of the vertebrae differs from human to human as the lower 2 parts, sacral and coccygeal bone may vary in length), a part of the rib cage (12 pairs of ribs and the sternum), and the skull (22 bones and 7 associated bones).
The bones of the thorax, called the "thoracic skeleton" is a component of the axial skeleton. It consists of the ribs and sternum . The ribs of the thorax are numbered in ascending order from 1–12. 11 and 12 are known as floating ribs because they have no anterior attachment point in particular the cartilage attached to the sternum, as 1 ...
The mediastinum comprises those organs which lie in the centre of the chest between the lungs. The cavity also contains two openings one at the top, the superior thoracic aperture also called the thoracic inlet , and a lower inferior thoracic aperture which is much larger than the inlet.
The rib cage or thoracic cage is an endoskeletal enclosure in the thorax of most vertebrates that comprises the ribs, vertebral column and sternum, which protect the vital organs of the thoracic cavity, such as the heart, lungs and great vessels and support the shoulder girdle to form the core part of the axial skeleton.
The hollow organs of the abdomen are the stomach, intestines, gallbladder, bladder, and rectum. [6] In the thoracic cavity , the heart is a hollow, muscular organ. [ 7 ] Splanchnology is the study of the viscera. [ 8 ]