The Sphenoid

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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 through 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