SPHENOID BONE. 153 



depression, the scaphoid fossa, from which arises the Tensor Palati, and above 

 which is seen the posterior orifice of the Vidian canal. The outer surface of 

 this plate forms part of the pterygoid fossa, the inner surface forming the outer 

 boundary of the posterior aperture of the nares. The Superior Constrictor of 

 the pharynx is attached to its posterior edge. The two pterygoid plates are 

 separated below by an angular interval, in which the pterygoid process, or 

 tuberosity, of the palate bone is received. The anterior surface of the ptery- 

 goid process is very broad at its base, and forms the posterior wall of the 

 spheno-rnaxillary fossa. It supports Meckel's ganglion. It presents, above, 

 the anterior orifice of the Vidian canal ; and below, a rough margin, which 

 articulates with the perpendicular plate of the palate-bone. 



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 th*e 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 sphenoid on 

 the inner. Fig. 104. Plan of the Development of the 



Development. The sphenoid bone is Sphenoid. By ten Centres, 



developed by ten centres, six for the pos- 

 terior sphenoidal division, and four for 

 the anterior sphenoid. The six centres 

 for the posterior sphenoid are one for 

 each greater wing and external pterygoid 

 plate ; one for each internal pterygoid 

 plate ; two for the posterior part of the 

 body. The four for the anterior sphenoid 

 are, one for each lesser wing and anterior 



part of the body, and one for each j&^ sj&nioi&l **& 



sphenoidal turbinated bone. Ossification 

 takes place in these pieces in the follow- 

 ing order : the greater wing and external pterygoid plate are first formed, ossifio 

 granules being deposited close to the foramen rotundum on each side, at about 

 the second month of fcetal life ; from thence ossification spreads outwards into 

 the great wing, and downwards into the external pterygoid plate. Each inter- 

 nal pterygoid plate is then formed, and becomes united to the external about 

 the middle of fcetal 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 fcetal life, into a single piece, which remains un-united 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 fcetal 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 articulation with each bone is shown in the accompanying figures. 



