THE, SPHENOID BONE. 121 
side of the spine the course of the chorda tympani nerve is indicated by a groove 
(Lucas). The second fifth of the convex border of the crescent is fused to the side 
of the body and united below with the root of the pterygoid process. The angle 
formed by the union of the great wing with the side of the body posteriorly corre- 
sponds to the hinder end of the carotid groove, the outer lip of which is formed by 
a projecting lamina called the lingula. The remaining three-fifths of the convex 
border is divisible into two nearly equal parts; the inner is a free, curved, sharp 
margin, which forms.the inferior margin of the sphenoidal fissure (fissura orbitalis 
superior), the cleft which separates the great wing from the lesser wing, and which 
establishes a wide channel of communication between the middle cranial fossa and 
the cavity of the orbit, transmitting the third, fourth, ophthalmic division of the 
fifth, and the sixth cranial nerves, together with the ophthalmic veins. Wide of 
the sphenoidal fissure this edge becomes broad and serrated, articulating with the 
frontal bone internally, and at the part corresponding to the anterior horn of the 
crescent, by a surface of variable width, it unites with the anterior inferior angle 
of the parietal bone. The eaternal border corresponds to the concave side “of 
the crescent, and is serrated for articulation with the squamous temporal, being 
thin and bevelled at the expense of its outer surface above and externally, and 
broad and thick behind as it passes towards the alar spine. The superior or 
cerebral surface is concave from behind forwards, and in its fore part from side to 
side also; it forms a considerable part of the floor of the middle cranial fossa, and 
bears the impress of the convolutions of the extremity of the temporal lobe of the 
cerebrum which rests upon it; towards its outer side it is grooved obliquely by an 
anterior branch of the middle meningeal artery. The following foramina pierce 
the great wing: close to and in front of the alar spine is the foramen spinosum 
for the transmission of the middle meningeal artery and its companion vein, 
together with a recurrent branch from the third division of the V. nerve. In 
front of and internal to this, and close to the posterior free border, is the 
foramen ovale, of large size and elongated form. This gives passage to 
the motor root and inferior sensory division of the V. nerve, and admits 
the small meningeal branch of the middle meningeal artery; a small emissary 
vein from the cavernous sinus usually passes through this foramen and 
occasionally also the small superficial petrosal nerve. Near the fore part 
of the root of the great wing, and just below the sphenoidal fissure, is the 
foramen rotundum, of smaller size and circular form. Through this the second 
division of the V. nerve escapes from the cranium. Occasionally there is a small 
canal—the foramen of Vesalius—which pierces the root of the great wing to the 
inner side of the foramen ovale. This opens below into the scaphoid fossa at the 
base of the internal pterygoid plate, and transmits a small vein. Occasionally there 
is a small foramen (canaliculus innominatus) to the inner side of the foramen 
spinosum for the transmission of the small superficial petrosal nerve. 
The outer surface of the great wing is divided into three well-marked areas; of 
these the upper two are separated by an oblique jagged ridge, the malar crest 
(margo zygomaticus), for articulation with the orbital process of the malar bone. 
The lower part of this ridge may occasionally articulate with the malar process of 
the superior maxilla. Of these two areas the orbital (facies orbitalis) is directed 
forwards and a little inwards; of quadrilateral shape, it forms the back and outer 
wall of the orbit; plane and smooth, it is bounded behind by the sharp inferior 
free margin of the sphenoidal fissure, towards the inner extremity of which a 
pointed spine for the attachment of the inferior common ligament of origin of the 
ocular muscles can usually be seen. It is limited superiorly by the edge of a rough 
triangular area which articulates with the frontal bone ; anteriorly by the malar crest ; ; 
whilst inferiorly a free, well-defined horizontal margin constitutes the posterior and 
external boundary of the spheno-maxillary fissure (fissura orbitalis inferior), which 
separates this part of the bone from the orbital plate of the superior mavxilla. 
Below this border there is a grooved surface which leads inwards toward the orifice 
of the foramen rotundum. In the articulated skull this forms part of the posterior 
wall of the spheno-maxillary fossa. 
To the outer side of the malar crest, which bounds it in front, is the temporal 
