58 THE BONES. 



bone by a smooth excavation to which Rigot has given the name of carotid fossa. 

 The external is also prolonged on the exterior surface of the sphenoid, by a short 

 and wide fissure ; it lodges the inferior maxillary nerve. Outside this is another 

 very narrow notch, intended for the passage of the middle meningeal artery. 

 The fibro-cartilaginous substance that partly fills the occipito-spheno-temporal 

 hiatus, transforms these notches into foramina, the first of which is named the 

 carotid canal ; the second, the foramen ovale ,• and the third, the foramen spinosum. 

 The inferior border, also concave, is likewise divided into three portions, a middle 

 and two lateral. The first is thick, and formed by the inferior extremity of the 

 body ; it is excavated by two large cavities belonging to the sphenoidal sinus. 

 These cavities are separated from one anotheV by a vertical osseous plate, often 

 perforated, which, at an early period, is fused with the perpendicular lamina of 

 the ethmoid bone. The very thin lateral portions form part of the circum- 

 ference of the wings ; they are notched near their union with the middle piece 

 to assist in the formation of the orbital foramen. The two lateral borders are 

 thin and convex in their anterior half, as is also the contour of the wings, which 

 are mortised in the frontal bone. For the remainder of their extent they are 

 thick, denticulated, and bevelled at the expense of the external plate, to articulate 

 with the squamous portion of the temporal bone. 



Structure. — This bone is compact on its sides, and spongy in its middle part ; 

 inferiorly, it is excavated by the sphenoidal sinuses. 



Development. — It is developed from two principal nuclei of ossification ; a 

 superior forms the subsphenoidal process and the canal of the same name, the 

 Vidian fissure, pituitary fossa, fissures of the internal face, and the most posterior 

 of the great supra-sphenoidal canals ; the other, the inferior, forms that portion 

 of the body hollowed by the sinuses, the lateral alje,^ and the optic fossa and 

 canals. In meeting each other, these centres form the Vidian canal and the two 

 anterior supra-sphenoidal canals. They are not consolidated with each other 

 until a very late period ; for which reason they are sometimes described as two 

 distinct bones. M. Tabourin has even proposed to attach the description of the 

 inferior sphenoid to that of the ethmoid, because it is united with this bone a 

 long time before it is joined to the superior portion.^ 



Differential Characters in the Sphenoii) Bone of other Animals. 



A. Ox. — In the Ox, the subsphenoidal or pterygoid processes are large and thin The 

 subsphenoidal canal is absent. The sella Turcica is deep, and the bony projection separating 

 it from the basilar process is very high. The three supra- splienoidal canals are converted into 

 a single, but wide one. There are no notches in the superior border, for the passage of tlie 

 internal carotid and spheno-spinous arteries. The oval foramen is entirely coufiued to this 

 bone. 



B. Sheep. — In theS^^fp, the osseous prominence that limits the pituitary fossa posteriorly 

 forms a lamina curving forwards, and prolonged at its extremities into two points, which 

 constitute the posterior clinoid processes. 



C. Camel.— The sphenoid is longer and thicker than in the Ox. The subsphenoidal 

 or pterygoid processes are narrow and very thick. The oval foramen is relatively small. The 

 optic canals are covered at their internal opening by a bony plate. The optic fossa is nearly 

 on a level with the pituitary fossa. 



D- Pig. — The sphenoid of the Pig is very short, but the subsphenoidal processes are 

 extraordinarily developed, and flattened before and behind. There is no subsphenoidal canal, 

 and the sella Turcica is deep, and limited behind by a very salient crest. A single canal 



' These wings are not analogous to those portions of the sphenoid bone in Man bearing the 

 same name. They are the processes of Ingrassias enormously developed. 



* Tabourin, Journal de MM. V^ttfrinaire, p. 229. Published at Lyons, 1845. 



