THE SPHENOID 



65 



the superior orbital (or sphenoidal) fissure, the elongated opening between the small and great 

 wings. The anterior border is serrated for articulation with the orbital plate of the frontal, 

 and the posterior border, smooth and rounded, is received into the Sylvian fissure of the cere- 

 brum. Moreover, the posterior border forms the boundary between the anterior and middle 

 cranial fossae and is prolonged at its medial extremity to form the anterior clinoid process, 

 which gives attachment to the tentorium cerebelli and the interchnoid ligaments. Between 

 the tuberculum sellse and the anterior chnoid process is a semicircular notch which represents 

 the termination of the carotid groove. It is sometimes converted into a foramen, the carotico- 

 clinoid foramen, by a spicule of bone which bridges across from the anterior clinoid to the middle 

 clinoid process; the latter is a small tubercle frequently seen on each side, in front of the hypo- 

 physeal fossa, and slightly posterior to the tuberculum seUse; the foramen transmits the internal 

 carotid artery, and the spicule of bone which may complete the foramen is formed by ossi- 

 fication of the carotico-clinoid ligament. 



The great or temporal wings [alse magnse], arising from the lateral surface of 

 the body, extend laterally and then upward and forward. The posterior part 

 is placed horizontally and projects backward into the angle between the squamous 

 and petrous portions of the temporal bone. From the under aspect of its pointed 

 extremity the spine, which is grooved medially by the chorda tympani nerve 

 (Lucas), projects downward. The spine serves for the attachment of the spheno- 

 mandibular ligament and a few fibres of the tensor veli palatini. Each wing 

 presents for examination four surfaces and four borders. 



Fig. 82. — Right Half of Sphenoid. (Anterior view.) 



( 



Temporal surface 



Ridge which forms the upper bound- 

 ary of the inferior orbital fissure 



Sphenoidal crest 

 Sphenoidal sinus 



Ext/ pterygoid muscle, 

 The spine 



The cerebral or superior surface is smooth and concave. It enters into the 

 formation of the middle cranial fossa, supports the temporo-sphenoidal lobe of 

 the cerebrum, and presents several foramina. At the anterior and medial 

 part is the foramen rotundum for the second division of the fifth nerve, and 

 behind and lateral to it, near the posterior margin of the great wing, is the large 

 foramen ovale, transmitting the third division of the fifth, the small meningeal 

 artery, and an emissary vein from the cavernous sinus. 



Behind and lateral to the foramen ovale is the small circular foramen spinosum, sometimes 

 incomplete, for the passage of the middle meningeal vessels, and the recurrent branch of the 

 third division of the fifth. Between the foramen ovale and the foramen rotundum is the incon- 

 stant foramen Vesalii, which transmits a small emissary vein from the cavernous sinus; and on 

 the plate of bone, behind and medial to the foramen ovale (spheno-petrosal lamma), a minute 

 canal is occasionallv seen — the canaliculus innominatus — through which the small superficial 

 petrosal nerve escapes from the skull. When the canaliculus is absent, the nerve passes through 

 the foramen ovale. 



The anterior surface looks medially and forward and consists of two divisions — 

 a quadrilateral or orbital surface, which forms the chief part of the lateral wall of 

 the orbit, and a smaller, inferior or spheno -maxillary surface, situated above the 

 pterj^goid process and perforated ty the foramen rotundum; this inferior part 

 forms the posterior wall of the pterygo-palatine fossa. 



The lateral or squamo-zygomatic surface is divided by a prominent infra- 

 temporal ridge into a superior portion, which forms part of the temporal fossa and 

 affords attachment to the temporal muscle, and an inferior part, which looks 

 downward into the zj-gomatic fossa and gives attachment to the external pterygoid 

 muscle; the inferior "^part joins the lateral surface of the lateral pterygoid plate 

 and presents the inferior orifices of the foramen ovale, foramen spinosum, and 

 foramen of Vesalius. 



