192 BONES OF THE CRANIUM. 



portions. Its development takes place from three centres of 

 ossification, one for the middle septum, and one for each, 

 lateral half. Ossification commences first in the lateral 

 portions, about the fifth month, (seen in the os-planum 

 first.) The middle part is not ossified till after birth, and 

 the cells are not complete till about the fifth or sixth year. 

 Before this period they are Ml, solid, and entirely cartila- 

 ginous. It is articulated with two bones of the cranium 

 the frontal and sphenoid, and 11 of the face, viz: the 2 

 superior maxillary, 2 lachrymal, 2 nasal, 2 palate, 2 inferior 

 turbinated, and the vomer. 



Sphenoid Bone (o$qv, a wedge.) The Sphenoid bone re- 

 ceives its name from the manner in which it is wedged in 

 or surrounded by all the bones of the cranium. Its situa- 

 tion is at the base of the cranium, stretching transversely 

 from side to side. Its form has been compared to the 

 bat, to which there is some resemblance, when the ethmoid 

 is attached. It is divided into a body and processes. The 

 processes constitute the wings and feet of the bat. 



The body occupies the centre of the bone, and presents 

 upon its anterior surface the azygos process, which articu- 

 lates with the superior end of the vomer. A small groove 

 for vessels is seen on each side of this process. The poste- 

 rior surface is flat and rough, for articulation with the 

 cuneiform process of the occipital bone. On the superior 

 surface there is a deep cavity called the sella turcica. This 

 is perforated by foramina for the passage of vessels, and 

 lodges the pituitary gland. It is bounded by a thin plate 

 of bone which rises almost perpendicularly at its posterior 

 part, and terminates in two processes called the posterior 

 dinoid, to which the tentorium is attached. 



At the anterior part of the sella turcica is an eminence 

 called the olivary, where is also seen a groove marking the 

 course of the optic nerves. The sides of the sella turcica, 

 are grooved for the internal carotid artery. 



From the superior and outer extremities of the body, 

 proceed transversely outwards, two long and thin pro- 

 cesses called the alce-minores 3 the lesser wings or apopJiyses 



