Topographical  Landmarks:

• acanthion – midline junction of the upper lip and nose
• alveolar processes – the junction of the 2 maxillary bones and the center of the mandible, in between the front two teeth
• auricle (pinna) – large flap of cartilage commonly referred to as the ear
• base of the orbit – bony rim surrounding each eye
• external acoustic (auditory) meatus (EAM) – external opening into the ear canal
• glabella – smooth, triangular area superior to the bridge of the nose and between the eyebrows
• gonion – lower, posterior angle seen on each side of the jaw or mandible; angle of the mandible
• infraorbital margin – inferior rim of the orbital base
• inoin – prominent bump, midline at the back of the head; external occipital protuberance
• inner canthus – junction of the upper and lower eyelids, near the nose
• mental point – midpoint of the chin; center of a flat, triangular region known as the mentum
• midlateral orbital margin – rim of bone near the outer corner of the eye
• nasion – slight depression at the bridge of the nose; marks the junction of the frontal and nasal bones
• superciliary ridge (arch) – ridge of bone found over each eye and under each eyebrow
• supraorbital groove – small depression directly above each superciliary arch; corresponds with the highest level of the facial bones and the floor of the anteroir fossa of the cranium
• supraorbital margin – superior rim of the orbital base
• top of ear attachment (TEA) – junction of the most superior portion of the ear and the scalp; corresponds with the level of the petrous ridges
• tragus – small flap of cartilage projecting over the external auditory meatus; auricular point
• outer canthus – lateral junction  of the upper and lower eyelids
• vertex – most superior point of the head

Positioning Lines and Planes:

• acanthiomeatal line (AML) – extends from the EAM to the acanthion
• glabelloalveolar line – connects glabella to anterior part of the alveolar process of  maxilla at the midline
• glabellomeatal line – extends from the EAM to glabella
• infraorbitomeatal line – extends from EAM to infraorbital margin; approximately a 7º angle between OML and IOML
• interpupillary line (interorbital line) – line connecting the two pupils or outer canthi of the eyes
• mentomeatal line – extends from EAM to mental point
• midsagittal plane – plane dividing the head (and body) into equal right and left halves
• orbitomeatal line (OML) – extends from EAM to outer canthus of eye; there is an  8ºdifference between the glabellomeatal and orbitomeatal lines.

Anatomy:

Skull – 8 bones make up the skull or cranium.  These include: frontal, right and left parietals, occipital, ethmoid, sphenoid, and right and left temporals.  The frontal, parietals, and occipital bones make up the calvarium or skull cap.  The temporals, ethmoid and sphenoid bones make up the cranial floor.

Sutures – There are four major sutures.  They are the sagittal, coronal, lambdoidal, and squamous.  Sutures are synarthrodial joints (immovable).  The junctions of the sagittal suture with the coronal and lambdoidal sutures are called the anterior and posterior fontanels, respectively.  Fontanels are the “soft spots” on an infant’s skull that allow for rapid brain growth.  In the adult the anterior fontanel is called the bregma and the posterior fontanel is called the lambda.

Facial Bones – There are a total of14 facial bones.  These include: right and left maxilla, right and left palatine, right and left zygomatic, right and left lacrimal, right and left nasal, right and left inferior nasal concha, the vomer and the mandible.  In addition to assisting in the formation of the mouth, nasal cavity, and orbits, the facial bones serve to protect the structures they house, such as the eyes.  With the exception of the mandible, the facial bones articulate with one another and the cranial bones in synarthrodial joints called sutures.  Gomphoses is the term for the synarthrodial joint formed by the teeth and the mandible and maxillae.  The mandible forms the only two movable (diarthrotic) joints in the cranium at its articulation with the temporal bones.  These joints are known as temporomandibular joints (TMJ’s) and allows ellipsoidal movement.

Sinuses – There are four pairs of paranasal sinuses.  They are the frontal sinuses, maxillary sinuses, ethmoid sinuses, and sphenoid sinuses.  The sphenoid may not always be paired, depending on the presence of a thin bony septum.