Head
* Major compartments
The head is composed of a series of compartments, which are formed by bone and soft tissues. They are:
- the cranial cavity,
- two ears,
- two orbits,
- two nasal cavities, and
- an oral cavity
The cranial cavity is the largest compartment and contains the brain and associated membranes (meninges).
Most of the ear apparatus on each side is contained within one of the bones forming the floor of the cranial cavity. The external parts of the ears extend laterally from these regions.
The two orbits contain the eyes. They are cone-shaped chambers immediately inferior to the anterior aspect of the cranial cavity, and the apex of each cone is directed posteromedially. The walls of the orbits are bone, whereas the base of each conical chamber can be opened and closed by the eyelids.
The nasal cavities are the upper parts of the respiratory tract and are between the orbits. They have walls, floors, and ceilings, which are predominantly composed of bone and cartilage. The anterior openings to the nasal cavities are nares (nostrils), and the posterior openings are choanae (posterior nasal apertures).
Continuous with the nasal cavities are air-filled extensions (paranasal sinuses), which project laterally, superiorly, and posteriorly into surrounding bones. The largest, the maxillary sinuses, are inferior to the orbits.
The oral cavity is inferior to the nasal cavities, and separated from them by the hard and soft palates. The floor of the oral cavity is formed entirely of soft tissues.
The anterior opening to the oral cavity is the oral fissure (mouth), and the posterior opening is the oropharyngeal isthmus. Unlike the nares and choanae, which are continuously open, both the oral fissure and oropharyngeal isthmus can be opened and closed by surrounding soft tissues.
Sources :
- Gray's Anatomy for Students, 2nd Edition ( 792 – 793 – 794 – 795 - 796 ) .
- Gray's Anatomy for Students, 2nd Edition ( 792 – 793 – 794 – 795 - 796 ) .
By Richard Drake PhD , A. Wayne Vogl PhD , Adam W. M. Mitchell MB
Copyright © 2009 by Churchill Livingstone
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