^10 FOSSIL REPTILES. 



dean bones are united one to another under the body of the 

 bone, to form the roof of the hinder nostrils. They unite also 

 below by a suture to form the floor of this same tube, and they 

 extend horizontally into a large wing, or broad surface, in 

 which the pterygoidean muscles are inserted above, and which 

 the membrane of the palate doubles below. 



One ridge or process from their roof, corresponding to 

 another of their floor, divides the nasal tube in two. Their 

 upper lamina, or plate, proceeds forward in the form of two 

 demi-cylinders to form again the roof of the double tube of the 

 back nostrils over that part where the palatines constitute its 

 floor, as far as the descending apophysis of the anterior 

 frontals, and even by the internal face, a little in front into the 

 cavity of the nose. 



The body of the sphenoid gives ris'e to no difficulty. It is 

 situated at the centre of the floor of the cranium, is slightly 

 concave, supporting the part of the brain placed behind the 

 optic tubercles, articulating by its sides with the temporal 

 wings in front, behind with the petrous processes, and by its 

 posterior extremity with the basilary or lower occipital bone, 

 descending between this occipital and the ossa pterygoidea, so 

 as to shew itself externally only by a small surface below the 

 lower occipital. An open canal in this surface traverses the 

 entire body of the bone, and opens in front by two branches 

 into a wide funnel, where the pituitary gland is lodged. In 

 front of this funnel the sphenoid gives out a vertical truncated 

 lamina which enters into the composition of the interorbitary 

 partition, and which is the only osseous part of it. 



Above this lamina is an empty space, the sides of which are 

 formed by the temporal wings, and the vault by the frontal 

 bone. In the fresh subject, the membranous and cartilaginous 

 interorbitary partition ends at the middle of this space, and 

 bifurcates for the purpose of closing it. 



It is through the upper part of this space that the olfactory 

 nerves pass ; the optic pass through the middle. Some vessels 



