THE SPHENOID 



63 



face presents the follo\ving points for examination : In front is seen a prominent 

 spine, the ethmoidal spine, which articulates with the hinder edge of the cribri- 

 form plate of the ethmoid. The surface behind this is smooth and frequently 

 presents two longitudinal grooves, one on either side of the median line, for the 

 olfactory bulbs; it is limited posteriorly by a ridge, the limbus sphenoidalis, 

 which forms the anterior border of the narrow transverse optic groove [sulcus 

 chiasmatis], above and behind which lies the optic commissure. The groove 

 terminates on each side in the optic foramen, which perforates the root of the 

 small wing and transmits the optic nerve and the ophthalmic arter3^ Behind the 

 optic groove is the tuberculum sellae, indicating the line of junction of the two 

 parts of which the body is formed (pre- and post-sphenoid) ; and still further 

 back, a deep depression, the hjrpophyseal fossa [sella turcica], which lodges the 

 hypophysis cerebri. The floor of the fossa presents numerous foramina for 

 blood-vessels, and at birth the superior orifice of a narrow passage called the 

 basi -pharyngeal canal opens on the tuberculum. The posterior boundary of the 

 fossa is formed by a quadrilateral plate of bone, the dorsum sellae (dorsum 



Small wing 



Fig. 79. — The Sphenoid, from Above. 

 Optic groove Ethmoidal spine 



Tuberculum se'lse Superior orbital fissure 



apophyseal fossa (sella 

 turcica) 



Articulation 

 \vith parietal 

 — Cerebral surface 

 of great wing 

 Foramen rotundum 



Foramen Vesalii 



Foramen ovale 



Foramen spinosum 



Carotid groove 

 Posterior petrosal process 



Posterior clinoid process 



Lingula 



ephippii), the posterior surface of which is sloped in continuation with the basilar 

 groove of the occipital bone. The superior angles of the plate are surmounted 

 by the posterior clinoid processes, which give attachment to the tentorium cere- 

 belli and the interclinoid ligaments. Below the clinoid process, on each side of 

 the dorsum sellse (sometimes at the suture between the sphenoid and apex of 

 petrosal), a notch is seen, converted into a foramen by the dura mater, for the 

 passage of the sixth cranial nerve, and at the inferior angle the posterior petrosal 

 process, which articulates with the apex of the petrous portion of the temporal 

 bone, forming the inner boundary of the foramen lacerum. The dorsum sellse 

 is slightly concave posteriorly (the clivus) and supports the pons Varolii and the 

 basilar artery. 



The inferior surface presents in the middle line a prominent ridge known as 

 the rostrum, which is received into a deep depression between the alse of the 

 vomer. On each side is the vaginal process of the medial pterygoid plate, 

 directed horizontally and medially, which, with the alse of the vomer, covers the 

 greater part of this surface. The remainder is rough and clothed by the mucous 

 membrane of the roof of the pharynx. 



The anterior surface is divided into two lateral halves by the sphenoidal 

 crest, a vertical ridge of bone continuous above with the ethmoidal spine, below 

 with the rostrum, and articulating in front with the perpendicular plate of the 

 ethmoid. The surface on each side presents a rough lateral margin for articula- 

 tion with the lateral mass of the ethmoid and the orbital process of the palate 

 bone. Elsewhere it is smooth, and enters into the formation of the roof of the 



