76 OSTEOLOGY. 



terior wall of the spheno-maxillary fossa; it supports Meckel's ganglion. It 

 presents, above, the anterior orifice of the Yidian canal ; and, below, a rough 

 margin, which articulates with the perpendicular plate of the palate bone. 



Development. The sphenoid bone is developed by ten centres, six for the pos- 

 terior sphenoidal division, and four for the anterior sphenoidal. The six centres 

 for the posterior sphenoidal division are, one for each greater wing and external 



pterygoid plate ; one for each internal ptery- 



Fig. 37. Plan of the Development of goid plate ; two for posterior part of the 

 Sphenoid. By Ten Centres. body. The four for the anterior sphe- 



noidal are, one for each lesser wing and 

 anterior part of the body; and one for 

 each sphenoidal turbinated bone. Ossifi- 

 cation takes place in these pieces in the 

 following order: the greater wing and ex- 

 ternal pterygoid plate are first formed, 

 ossific granules being deposited close to the 

 foramen rotundum on each side, at about 

 the second month of foetal life ; ossification 

 iLnated lone spreading outwards into the great wing, 



and downwards into the external pterygoid 

 plate. Each internal pterygoid plate is 

 then formed, and becomes united to the external about the middle of foetal life. 

 The two centres for the posterior part of the body appear as separate nuclei, side 

 by side, beneath the sella Turcica ; they join about the middle of foetal life into 

 a single piece, which remains ununited to the rest of the bone until after birth. 

 Each lesser wing is formed by a separate centre, which appears on the outer side 

 of the optic foramen, at about the third month; they become united and join 

 with the body at about the eighth month of foetal life. At about the end of the 

 third year, ossification has made its appearance in the sphenoidal spongy bones. 

 At birth, the sphenoid consists of three pieces ; viz., the greater wing and 

 pterygoid processes on each side ; the lesser wings and body united. At the first 

 year after birth, the greater wings and body are united. From the tenth to the 

 twelfth year, the spongy bones are partially united to the sphenoid, their junction 

 being complete by the twentieth year. Lastly, the sphenoid joins the occipital. 



Articulations. The sphenoid articulates with all the bones of the cranium, and 

 five of the face ; the two malar, two palate, and vomer. The exact extent of articu- 

 lation with each bone is shown in the accompanying figures. 



Attachment of Muscles. The Temporal, External pterygoid, Internal pterygoid, 

 Superior constrictor, Tensor palati, Laxator tympani, Levator palpebrae, Obliquus 

 superior, Superior rectus, Internal rectus, Inferior rectus, External rectus. 



THE SPHENOIDAL SPONGY BONES. 



The Sphenoidal Spongy Bones are two thin, curved plates of bone, which exist 

 'as separate pieces until puberty, and occasionally are not joined to the sphenoid 

 in the adult. They are situated at the anterior and inferior part of the body of 

 the sphenoid, an aperture of variable size being left in their anterior wall through 

 which the sphenoidal sinuses open into the nasal fossae. They are irregular in 

 form, and taper to a point behind, being broader and thinner in front, Their 

 inner surface, which looks towards the cavity of the sinus, is concave ; their outer 

 surface convex. Each bone articulates in front with the ethmoid, externally with 

 the palate ; behind, its point is placed above the vomer, and is received between 

 the root of the pterygoid process on the outer side, and the rostrum of the sphe- 

 noid on the inner. 



