THE SPHENOID BONE 



149 



Between the eighteenth and twenty-fifth years this becomes ossified, ossification 

 commencing above and extending downward. 



The anterior surface of the body (Fig. 146) presents, in the middle line, a vertical 

 crest, the sphenoidal crest, which articulates with the perpendicular plate of the 

 ethmoid, and forms part of the septum of the nose. On either side of the crest 

 is an irregular opening leading into the corresponding sphenoidal air sinus. These 

 sinuses are two large, irregular cavities hollowed out of the interior of the body 

 of the bone, and separated from one another by a bony septum, which is commonly 

 bent to one or the other side. They vary considerably in form and size, 1 are 

 seldom symmetrical, and are often partially subdivided by irregular bony lamina?. 

 Occasionally, they extend into the basilar part of the occipital nearly as far as the 

 foramen magnum. They begin to be developed before birth, and are of a consid- 

 erable size by the age of six. They are partially closed, in front and below, by tw r o 

 thin, curved plates of bone, the sphenoidal conchse (see page 152), leaving in the 

 articulated skull a round opening at the upper part of each sinus by which it com- 



Anterior clinoid -process 



Posterior clinoid process ] Notch /or abducent 



nerve 

 Superior 



'oramen rotundum 



Scaphoid fossa 

 Pterygoid foss 



I*U 



ft 



Spina angularis 



terygoid canal 

 Lateral pterygoid lamina 

 Medial plerygoid lamina 



Hamuius 



Rostrum 

 Fia. 147 Sphenoid bone. Upper and posterior surfaces. 



unicates with the upper and back part of the nasal cavity and occasionally with 

 the posterior ethmoidal air cells. The lateral margin of the anterior surface is 

 serrated, and articulates with the lamina papyracea of the ethmoid, completing 

 the posterior ethmoidal cells; the lower margin articulates with the orbital process 

 of the palatine bone, and the upper with the orbital plate of the frontal bone. 



The inferior surface presents, in the middle line, a triangular spine, the sphenoidal 

 rostrum, which is continuous with the sphenoidal crest on the anterior surface, 

 and is received in a deep fissure between the alse of the vomer. On either side of 

 the rostrum is a projecting lamina, the vaginal process, directed medialward from 



e base of the medial pterygoid plate, with which it will be described. 



The Great Wings (alee magnce}. The great wings, or ali-sphenoids, are two 

 strong processes of bone, which arise from the sides of the body, and are curved 

 upward, lateralward, and backward; the posterior part of each projects as a tri- 

 angular process which fits into the angle between the squama and the petrous 



1 Aldren Turner (op. cit.) gives the following as their average measurements: vertical height, '/s inch; antero-posterior 

 epth, '/s inch; transverse breadth, % inch. 



