The Sphenoid

The Sphenoid is one of the more difficult bones to describe and invision. It has a number of features and projections, which allow it to be seen from various views of the skull. It is a single bone that runs thrugh the mid-sagittal plane and aids to connect the cranial skeleton to the facial skeleton. It consists of a hollow body, which contians the Sphenoidal Sinus, and three pairs of projections: the more superior Lesser Wings, the intermediate Greater Wings, and the most inferior projecting Pterygoid Processes. Internally upon the body is the Sella Turcica where the pituitary gland rests in life. The smaller lesser wings posssesses the Optic Foramen through which the optic or second cranial nerve passes before giving rise to the eye. The Supra- Orbital Fissure separates the lesser wing superiorly from the greater wing below and can best be viewed on the posterior wall of each eye orbit. The left and right greater wings assist in forming the posterior wall of each of the eye orbits where it forms an Orbital Plate. In addition the external surface of the greater wing can be viewed in the the lateral view of the cranium in an area called the Pterion Region. Just inferior to the supra-orbital fissure near the body of the sphenoid, each of the greater wings also possess a Foramen Rotundum which in life transmits the maxillary branch of the fifth, or trigeminal, cranial nerve. Each of these wings also possesses a much larger Foramen Ovale more laterally, which transmits the the mandibular branch of the same nerve. More posteriorly is the smallest of the three pairs of foramena, the Foramen Spinosum which transmits the middle meningial vessels and nerve to the tissues covering the brain.

The left and right pterygoid processes project inferiorly from near the junction of each of the greater wings with the body of the sphenoid. These processes run along the posterior portion of the nasal passage toward the palate. Each process is formed from a Medial and Lateral Pterygoid Plate to which the respective medial and lateral pterygoid muscle is attached during life. The muscles run from these attachments to the internal, or medial surface, of the mandible in the area of the gonial angle. In life the muscles assist in creating the grinding motion associated with chewing.

The sphenoid touches, or articulates with, the following bones: Vomer – Ethmoid –Frontal – Occipital – Parietals Temporals – Zygomatics – Palatines.

The Sphenoid

Also called the Malars or Jugals, each cheek or zygomatic bone possesses three major processes which articulate with the bones which surround it. The Frontal Process of the zygomatic forms the lateral margin and wall of the eye orbit and projects superiorly to articulate with the zygomatic process of the frontal bone. This portion of the bone separates the eye orbit from the temporal fossa and possesses a posterior projecting edge called the Marginal Process. The Temporal Process of the zygomatic runs lateral and posterior toward an articulation with the zygomatic process of the temporal bone. Together these two processes assist in forming the zygomatic arch which serves as the attachment for the masseter muscle in life, one of the primary muscles used in mastication. The temporal muscle runs beneath the arch and is also a primary mover of the mandible in chewing. The Maxillary Process of the zygomatic articulates with the zygomatic portion of the maxilla by way of the Zygo-Maxillary Suture.

The zygomatics touch, or articulate with, the following bones: Frontal - Sphenoid - Maxillae - Temporals .

The Zygomatic Bones

The Mandible or lower jaw consists to four major portions, a left and right Mandibular Ramus and the left and right Body. The Alveolar Process of the body is that portion of the mandible which contains the lower dentition. The junction of the ramus and the body occurs at the Gonial Angle where externally one of the masseter muscles is attatched. The left and right masseters make up a set of two sets of muscels used in chewing. At the gonial angle on the internal surface the Pterygoid Attachements are found. These attachements are for the medial and lateral pterygoid muscles which assist in the grinding motion of chewing. The external surface of the mandibular body possesses the Mental Foramen and at the midline, the Mental Protuberance or chin. The internal surface of the body possesses the Lingual Foramen, the Mandibular Canal, and the longitudinal running Mylo-Hyoid Ridge. The Genio Tubercle is located in the mid- sagittal plane on the internal surface of the mandible. The superior margin of each ramus possesses both a Mandibular Condyle or Head, for articulaltion with the temporal bone at the tempro-mandibular joint, and the Coronoid Process, for the attachement of the temporalis muscle (one in the set of primary muscles used in mastication). The mandible articulates with each of the Maxillae by way of their contained respective lower and upper dentition.

The mandible touches, or articulates with, the following bones: Temporals – Maxillae.

The Mandible

The Maxillae

The Maxillae are the paired facial bones which contain the upper dention and thus form the upper jaw. Each is basicly hollow with a large Maxillary Sinus. A superior projection, the Frontal Process, assists in forming the lateral margin of the nasal aperture and ends by articulating with the frontal bone. An Orbital Plate forms the floor of the eye orbit, while the Zygomatic Process articuates with the zygomatic bone.

On the anteror surface of the bone, near the maxillo-zygomatic suture, ther is an Infra- Orbital Foramen. The Alveolar Process of the Maxilla contains the upper dentition and assists in giving rise to the Palatine Portion which forms the anterior half of the hard palate. The left and right Maxillae articulate with one another by way of the Inter-Maxillary Suture. The superior end of this suture frequently terminates with the Nasal Spine.

A maxilla touches, or articulates with, the following bones: Frontal – Ethmoid – Zygomatic – Vomer – Lacrimal – Maxilla – Nasal –

Palatine – Mandible – Inferior Nasal Concha.

The Palatine Bones are paired left and right and articulate with one another in the mid-sagittal plane at the Interpalatine Suture. Both bones assist in forming the posterior portion of the hard palate as well as a portion of the nasal cavity.

Each bone possesses a Horizontal Part, with an inferior surface which forms the posterior portion of the hard palate and a superior surface that assists in forming the posterior portion of the floor of the nasal cavity. The Vertical Part of each contributes to the lateral wall of the nasal cavity. Near the posterior junction of the Vertical and Horizontal Parts on the palatal surface is a Palatine Foramen. Each bone possesses a number of processes and articular surfaces which touch the bones that surround it.

A palatine touches, or articulates with, the following bones: Sphenoid – Ethmoid – Maxilla – Vomer - Palatine.

The Palatine Bones

The Vomer is a single relatively flat bone located in the mid-sagittal plane. It articulates with the perpendicular plate of the ethmoid superiorly and together aid in forming the nasal septum. While it is frequently deflected slightly to the left or right, in general the septum is aligned perpendicularly and divides the the nasal aperture into the the left and right nasal passages. In addition to the Perpendicular Portion, superiorly the Vomer mushrooms out into a pair of Alae which terminate and articulate with the sphenoid in a heart shaped process. Inferiorly the Vomer rests on both the maxillae and the palatines.

The vomer touches, or articulates with, the following bones: Sphenoid – Ethmoid – Palatines – Maxillae.

The Vomer Bone

Giallo : mascella

Marrone : mandibola