THE SPHENOID BONE. 123 
is seen the anterior opening of the Vidian canal. Below, the pterygoid plates are 
separated by an angular cleft, the pterygoid notch (fissura pterygoidea)~ in this is 
lodged the tuberosity of the palate bone, the margins of which articulate with the 
serrated edges of the recess. 
Connexions.— The sphenoid articulates with the occipital, temporals, parietals, frontal, 
ethmoid, sphenoidal turbinals, vomer, palate and malar bones, and occasionally with the superior 
maxillie. 
Architecture.—In the adult the body of the bone is hollow and encloses the sphenoidal air 
cells, usually two in number, separated by a septum. The arrangement and extent of these air 
cells vary ; sometimes they are multilocular, at other times simple, while occasionally they extend 
backwards into the basioccipital and outwards and downwards into the roots of the great wings 
and pterygoid processes. Cases are on record in which in the adult the body of the bone was not 
pneumatic. 
Variations.—Through imperfect ossification the foramen spinosum and foramen ovale are 
sometimes incomplete posteriorly. On the other hand, owing to the ossification of fibrous bands 
connecting the several bony points, anomalous foramina are frequently met with. Cases of 
persistence of the cranio-pharyngeal canal have been recorded. 
Ossification.—The sphenoid of man is formed by the fusion of two parts, the pre- 
sphenoid and the post-sphenoid, each associated with certain processes. In most mammals 
the orbito-sphenoids or lesser wings fuse with the pre-sphenoid, whilst the alisphenoids or 
greater wings, together with the internal pterygoid plate, ankylose with the post-sphenoid. 
The ossification of these several parts takes place in cartilage, with the exception of the 
internal pterygoid plate, which is developed from an independent centre in the connective 
tissue of the lateral wall of the oral cavity (Hertwig). 
At the end of the second month a centre appears in the root of the great wing between 
the foramen ovale and foramen rotundum ; from this the ossification spreads outwards and 
backwards and also downwards into the external pterygoid plate. Meanwhile two centres 
appear about the same time in the basi-sphenoid in relation to the floor of the sella turcica and 
on either side of the cranio-pharyngeal canal, around which they ossify, ultimately leading 
to the obliteration of this channel. Somewhat later a centre appears on either side, from 
which the lateral aspect of the body and the lingula are developed. Fusion between these 
four centres is usually complete by the sixth month. 
In the pre-sphenoid a pair of lateral nuclei make their appearance about the middle of 
the third month, just external to the optic 
foramina; from each of these the orbito- 
sphenoids (lesser wings) and their roots are 
developed. About the same time another 
pair of centres, placed mesial to the optic 
foramina, constitute the body of the pre- 
sphenoid. By the coalescence of these in 
front, and their ultimate union with the basi- 
sphenoid behind, a cartilaginous interval is 
enclosed, of triangular shape, which, however, 
becomes gradually reduced in size by the Fic. 94.—OssIFICATION OF SPHENOID. 
ingrowth of its margins so as to form two 4, Presphenoid; b, Orbito-sphenoids; c, Alisphenoids ; 
mesially-placed foramina, as may be frequently d, Internal pterygoid plates ; e, Basisphenoid. 
observed in young bones—one opening on the 
surface of the olivary eminence, the other being placed anteriorly (Lawrence, “ Proc. 
Soc. Anat.” Journ. Anat. and Physiol., vol. xxviii. p. 19). 
As has been said, the internal pterygoid plates are developed in membrane. Each is 
derived from a single nucleus which appears about the fourth month and fuses with the 
under surface of the great wing, there forming a groove, which is converted into the 
Vidian canal when the alisphenoid and internal pterygoid plates fuse later with the body 
of the post-sphenoid. 
At birth the sphenoid consists of three parts: one comprising the orbito-sphenoids 
together with the body of the pre-sphenoid and the basi-sphenoid, the others consisting of 
the alisphenoids, one on either side. Fusion of the latter with the former occurs near the 
end of the first year. The dorsum sella at birth consists of a cartilaginous plate which 
separates the body of the post-sphenoid from the basi-occipital. This slowly ossifies, but 
the cartilage does not entirely disappear till the age of twenty-five, by which time bony anky- 
losis of the basi-cranial axis is complete. Fora considerable time the under surface of the 
body of the pre-sphenoid displays a bullate appearance, with the sides of which the 
sphenoidal turbinated bones articulate. It is only after the seventh or eighth year is 
