80 



THE SKELETON 



The body is irrogulavly cuboiJal in sliai)e. Tlu' superior surface presents the 

 following points for exanhnation. In front, there is a prominent si»ine, which 

 is received ))etween the diverging ala? of the crista galli, and is known as the 

 ethmoidal spine. The surface behind this is smooth, and is formed l)y extensions 

 of the lesser or orliital wings; it frequently ]iresents two parallel longitudinal 

 grooves for the olfactory bull)S. This smootli surface is terminated l)y a ridge, the 

 fimbus, behind which 'is the optic groove lodging the optic chiasma, and leads on 

 each side into the optic foramen. The groove is bounded posteriorly by the 

 olivary eminence, a ridge of Inme indicating the line of union of the pre- and 

 post-sphenoid. Behind this ridge the bone i)resents a deep hollow, the pituitary 

 fossa, in which the pituitary body is lodged. The floor of this fossa i)resents 

 numerous foramina for blood-vessels, and at birth the superior orifice of a narrow 

 passage termed the cranio-pharyngeal canal. The j^ituitary fossa presents on 

 each side, slightly ]iosterior to the olivary eminence, a tubercle of variable size, the 

 middle clinoid process. This is occasionally prolonged to meet the anterior 

 clinoid process on the orbital wing. The posterior boundary is formed by a 

 quadrilateral plate of bone, the dorsum ephippii. The superior angles of this 

 plate are surmounted by the posterior clinoid processes, which give attachment 

 to the tentorium cerebelli. A little below the clinoid process, on each side of the 

 dorsum ephii)pii, there is a deep notch, converted into a foramen l)y the dura 



Fig. 30. — The Sphenoid. (Tiewed from above. 



OPTIC FORAMEN 

 SPHENOIDAL FISSURE 



FORAMEN ROTUNDUM 



FORAMEN OVALE 

 FORAMEN SPINOSUM 



SPINE OF THE SPHENOID 

 EXTERNAL PTERYGOID PLATE 



INTERNAL PTERYGOID PLATE 



PTERYGOID NOTCH 



HAMULAR PROCESS 



mater, for the passage of the sixth cranial nerve. The dorsum is slightly concave 

 posteriorly, and supports the basilar artery and the pons. 



The inferior surface of the body has a prominent median ridge, the rostrum, 

 which is received l)et\veen the alffi of the vomer. The rest of the surface is rough, 

 and covered l)y the mucous memljrane belonging to the roof of the pharynx. 



The anterior surface presents in the middle line a vertical ridge of bone, the 

 sphenoidal crest, which articulates with the peri)endicular plate of the ethmoid. 

 On each side of tlie crest is a groove which forms part of the roof of the nose; it is 

 bounded externally by a more or less circular orifice which leads into the sphe- 

 noidal sinuses. Still more externally is a rough area for articulation with the 

 lateral mass of the ethmoid. These sinuses are irregularly shaped, unsymmetrical 

 cavities, separated from one another by a thin vertical se]itum; in adult Iwnes they 

 may extend into the roots of the pterygoid processes, and even into the base of the 

 occipital bone. The sinuses communicate with the nasal fossa of their respective 

 sides. The lateral margins of the antei'ior surface are serrated for articulation with 

 the posterior border of the os planum on each side of the ethmoid. The su[)erior 

 mai'gin articulates with the cribriform plate of the ethmoid. 



The posterior surface or basi-sphcnoid is, in the adult, ankylosed to the basi- 

 occij)ital. The two bones are separated by a disc of hyaline cartilage until the 

 eighteenth year; by the twenty-fifth year ankylosis is complete. 



Tlie lateral surface enters into the formation of the jjosterior part of the inner 



