THE SKULL. 27 
Its lateral surfaces are mostly covered by the wings. They 
appear at the sides of the elevated cranial end of the dorsal 
surface as triangular areas. 
The caudal end is concave, rough, and has the form of the 
cranial end of the basilar part of the occipital. 
The cranial end is nearly square and rough for articulation 
with the body of the presphenoid. 
The Wing (alisphenoid ; ala magna of the human sphenoid) 
(Fig. 20, 6).—This is a thin quadrilateral plate of bone attached 
by its medial border to nearly the whole of the lateral surface 
of the body. Its middle portion lies nearly in the same plane 
as the body, but its ends are curved dorsad so that its internal 
surface is concave and its external surface is convex. The 
curvature is most pronounced near the long lateral border, so 
that this border forms nearly a semicircle. 
The internal surface supports the occipital lobe of the cere- 
brum. It is marked by a rounded groove (/) which is parallel 
with the lateral surface of the body. The dorsal margin of the 
groove projects mediad in the form ofa sharp ridge which is 
broadest caudad, where it often reaches nearly to the posterior 
clinoid process. The groove passes craniad into three fora- 
mina. The first (cranial) of these, the orbital fissure (2), is 
large and lies between the wing, the body, and the pterygoid 
process. It is incomplete, but is completed by the presphenoid. 
The second foramen is small and rounded; it is the foramen 
rotundum (7). The third, foramen ovale (4), is larger and 
oval and penetrates the wing through about the middle of its 
longitudinal axis. Another minute foramen penetrates the 
sphenoid between the wing and the body of the bone, just 
laterad of the tuberculum sella. This foramen is continuous 
craniad with a groove on the dorsal surface of the pterygoid 
process; the groove and foramen constitute the pterygoid 
canal. It transmits a nerve. 
The external surface shows the orbital fissure, the foramen 
rotundum and the foramen ovale, bounded ventrally by a sharp 
ridge, which is continued onto the pterygoid process. Between 
this ridge and the body the surface is longitudinally arenues 
for the tuba auditiva or Eustachian tube. 
