7.2 The skull  (Page 8/120)

Zygomatic bone

The zygomatic bone    is also known as the cheekbone. Each of the paired zygomatic bones forms much of the lateral wall of the orbit and the lateral-inferior margins of the anterior orbital opening (see [link] ). The short temporal process of the zygomatic bone projects posteriorly, where it forms the anterior portion of the zygomatic arch (see [link] ).

Nasal bone

The nasal bone    is one of two small bones that articulate (join) with each other to form the bony base (bridge) of the nose. They also support the cartilages that form the lateral walls of the nose (see [link] ). These are the bones that are damaged when the nose is broken.

Lacrimal bone

Each lacrimal bone    is a small, rectangular bone that forms the anterior, medial wall of the orbit (see [link] and [link] ). The anterior portion of the lacrimal bone forms a shallow depression called the lacrimal fossa    , and extending inferiorly from this is the nasolacrimal canal    . The lacrimal fluid (tears of the eye), which serves to maintain the moist surface of the eye, drains at the medial corner of the eye into the nasolacrimal canal. This duct then extends downward to open into the nasal cavity, behind the inferior nasal concha. In the nasal cavity, the lacrimal fluid normally drains posteriorly, but with an increased flow of tears due to crying or eye irritation, some fluid will also drain anteriorly, thus causing a runny nose.

Inferior nasal conchae

The right and left inferior nasal conchae form a curved bony plate that projects into the nasal cavity space from the lower lateral wall (see [link] ). The inferior concha is the largest of the nasal conchae and can easily be seen when looking into the anterior opening of the nasal cavity.

Vomer bone

The unpaired vomer bone, often referred to simply as the vomer, is triangular-shaped and forms the posterior-inferior part of the nasal septum (see [link] ). The vomer is best seen when looking from behind into the posterior openings of the nasal cavity (see [link] a ). In this view, the vomer is seen to form the entire height of the nasal septum. A much smaller portion of the vomer can also be seen when looking into the anterior opening of the nasal cavity.

Mandible

The mandible    forms the lower jaw and is the only moveable bone of the skull. At the time of birth, the mandible consists of paired right and left bones, but these fuse together during the first year to form the single U-shaped mandible of the adult skull. Each side of the mandible consists of a horizontal body and posteriorly, a vertically oriented ramus of the mandible    (ramus = “branch”). The outside margin of the mandible, where the body and ramus come together is called the angle of the mandible    ( [link] ).

The ramus on each side of the mandible has two upward-going bony projections. The more anterior projection is the flattened coronoid process of the mandible    , which provides attachment for one of the biting muscles. The posterior projection is the condylar process of the mandible    , which is topped by the oval-shaped condyle    . The condyle of the mandible articulates (joins) with the mandibular fossa and articular tubercle of the temporal bone. Together these articulations form the temporomandibular joint, which allows for opening and closing of the mouth (see [link] ). The broad U-shaped curve located between the coronoid and condylar processes is the mandibular notch    .