

THE SPHENOID BONE 151 







internal surface, for articulation with the sphenoidal angle of the parietal bone; 

 this region is named the pterion. Medial to this is a triangular, serrated surface, 

 for articulation with the frontal bone; this surface is continuous medially w r ith 

 the sharp edge, \vhich forms the lower boundary of the superior orbital fissure, 

 and laterally with the serrated margin for articulation with the zygomatic bone. 



The Small Wings (aloe panes'}. The small w y ings or orbito-sphenoids are two 

 thin triangular plates, which arise from the upper and anterior parts of the body, 

 and, projecting lateralward, end in sharp points (Fig. 145). 



Surfaces. The superior surface of each is flat, and supports part of the frontal 

 lobe of the brain. The inferior surface forms the back part of the roof of the orbit, 

 and the upper boundary of the superior orbital fissure. This fissure is of a triangular 

 form, and leads from the cavity of the cranium into that of the orbit: it is bounded 

 medially by the body; above, by the small wing; below, by the medial margin of 

 the orbital surface of the great wing; and is completed laterally by the frontal 

 bone. It transmits the oculomotor, trochlear, and abducent nerves, the three 

 branches of the ophthalmic division of the trigeminal nerve, some filaments from 

 the cavernous plexus of the sympathetic, the orbital branch of the middle menin- 

 geal artery, a recurrent branch from the lacrimal artery to the dura mater, and the 

 ophthalmic vein. 



Borders. The anterior border is serrated for articulation with the frontal bone. 

 The posterior border, smooth and rounded, is received into the lateral fissure of 

 the brain; the medial end of this border forms the anterior clinoid process, which 

 gives attachment to the tentorium cerebelli; it is sometimes joined to the middle 

 clinoid process by a spicule of bone, and when this occurs the termination of the 

 groove for the internal carotid artery is converted into a foramen (carotico-clinoid") . 

 The small wing is connected to the body by two roots, the upper thin and flat, 

 the lower thick and triangular; between the two roots is the optic foramen, for the 

 transmission of the optic nerve and ophthalmic artery. 



Pterygoid Processes (processus pterygoidei) . The pterygoid processes, one on 

 either side, descend perpendicularly from the regions where the body and great 

 wings unite. Each process consists of a medial and a lateral plate, the upper parts 

 of which are fused anteriorly; a vertical sulcus, the pterygopalatine groove, descends 

 on the front of the line of fusion. The plates are separated below by an angular 

 cleft, the pterygoid fissure, the margins of which are rough for articulation with 

 the pyramidal process of the palatine bone. The two plates diverge behind and 

 enclose between them a V-shaped fossa, the pterygoid fossa, which contains the 

 Pterygoideus internus and Tensor veli palatini. Above this fossa is a small, oval, 

 shallow" depression, the scaphoid fossa, which gives origin to the Tensor veli palatini. 

 The anterior surface of the pterygoid process is broad and triangular near its 

 root, where it forms the posterior wall of the pterygopalatine fossa and presents 

 the anterior orifice of the pterygoid canal. 



Lateral Pterygoid Plate. The lateral pterygoid plate is broad, thin, and everted; 

 its lateral surface forms part of the medial wall of the infratemporal fossa, and 

 gives attachment to the Pterygoideus externus; its medial surface forms part of 

 the pterygoid fossa, and gives attachment to the Pterygoideus internus. 



Medial Pterygoid Plate. The medial pterygoid plate is narrower and longer 

 than the lateral; it curves lateralw r ard at its lower extremity into a hook-like pro- 

 cess, the pterygoid hamulus, around which the tendon of the Tensor veli palatini 

 glides. The lateral surface of this plate forms part of the pterygoid fossa, the 

 medial surface constitutes the lateral boundary of the choana or posterior aperture 

 of the corresponding nasal cavity. Superiorly the medial plate is prolonged on to 

 the under surface of the body as a thin lamina, named the vaginal process, which 

 articulates in front with the sphenoidal process of the palatine and behind this 

 with the ala of the vomer. The angular prominence between the posterior margin 



