THE SPHENOID BONE 



91 



Along the outer margin of this groove, at its posterior part, is a ridge of bone 

 in the angle between the body and greater wing, called the lingula (lingula 

 sphenoidalis). 



The posterior surface, quadrilateral in form, is joined to the basilar process 

 of the occipital bone. During childhood these bones are separated by a layer 

 of cartilage; but later (between the eighteenth and twenty-fifth years) this becomes 

 ossified from above downward, and the two bones then form one piece. 



The anterior surface (Fig. 57) presents, in the median line, a vertical ridge of 

 bone, the ethmoidal crest (crista sphenoidalis), which articulates in front with the 

 perpendicular plate of the ethmoid, forming part of the septum of the nose (Fig. 

 57). On either side of it are irregular openings leading into the sphenoidal sinuses 

 (sinus sphenoidales), which are two large, irregular cavities of the hollowed out 

 interior of the body of the sphenoid bone, and separated more or less completely 

 from each other by a perpendicular bony septum (septum sinuum sphenoidalium). 

 Occasionally they extend into the basilar process of the occipital nearly as far 

 as the foramen magnum. Their form and size vary considerably; they are seldom 



Articulates with perpendicular 

 plate of ethmoid. 



Pterygoid ridge 



Internal pterygoid plate. 

 Hamular process.- 



FIG. 57 Sphenoid bone. Anterior surface. 1 



symmetrical, and are often partially subdivided by irregular, osseous laminae. 

 One or both sinuses may be absent. The septum is seldom quite vertical, being 

 commonly bent to one or the other side. These sinuses do not exist in very 

 young children, but appear, according to Laurent, in the seventh year. After 

 once appearing they increase in size as age advances. They are partially closed, 

 in front and below, by two thin, curved plates of bone, the sphenoidal turbinated 

 processes (conchae sphenoidales}. At the upper part of each is a round opening 

 (apertura sinus sphenoidalis}, by which the sinus communicates with the upper 

 and back part of the nose, and occasionally with the posterior ethmoidal cells 

 or sinuses. The lateral margins of the surface present a serrated edge, which 

 articulates with the os planum of the ethmoid, completing the posterior ethmoidal 

 cells; the lower margin, also rough and serrated, articulates with the orbital 

 process of the palate bone, and the upper margin with the orbital plate of the 

 frontal bone. 

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



1 In this figure both the anterior and inferior surfaces of the body of the sphenoid bone are shown, the bone 

 being held with the pterygoid processes almost horizontal. 



