BONES OF THE HEAD. ^ 25 



dinal sinuses; inferiorly there proceeds a ridge to the foramen mag- 

 num to which is attached the falx cerebelU. The concavity is thus 

 divided into four ; the two superior, containing the posterior lobes of 

 the cerebrum, and the two inferior the hemispheres of the cerebellum. 

 The two superior edges are deeply dentated and articulate with 

 the parietal ; the two inferior articulate with the temporal. On 

 each edge is a prominence called the jugular endnence^^ in front 

 of which is a fossa converted into the posterim- foramen lacerum^^ 

 by articulation, through which pass the internal jugular vein and the 

 eighth pair of nerves. Upon the inferior surface of this eminence is 

 inserted the rectus capitis lateralis. 



SPHENOID. 



Position, In the middle and anterior part of the base of the cra- 

 nium. Shaj^e. Resembles a bat ; consists of a body and four wings ; 

 a large and small one being placed on each side, besides two vertical 

 processes directed downwards. 



The body is in the centre and cuboidal in its shape. On its supe- 

 rior surface is a deep pit called sella turcica,''^ which contains the 

 the pituitary gland. This depression is overhung posteriorly by 

 the jjosterior clinoid process /^ on either side are two grooves called 

 sulci carotid, for the carotid arteries, and in front there is a promi- 

 nence called processus olivaris, upon which is a transverse groove 

 indicating the position of the chiasm of the optic nerves. 



On the anterior view of the body are the orifices of the two sphe- 

 noidal cells, separated by a ridge, upon which articulates the nasal 

 lamella of the ethmoid bone; they empty into the post. eth. cells and 

 do not exist in infancy. The inferior surface of the body has an ele- 

 vation in the middle line called the processus azygos, by which it ar- 

 ticulates with the lower two projections. Posteriorly, the surface is 



Fig. 11. 



