101 Sphenoid Bens. [Book IX. 



rfiinences, cavities, and meanders of the ethmoid bone 

 are covered with a continuation of the membrane of 

 the noftrils. The ufes of this bone are to fuftain the 

 anterior lobes of the brain ; to give paffage to the ol- 

 factory nerves, and attachment to the falx ; to enlarge 

 the organ of fmelling, by allowing the membrane of 

 the nofe a greater extent j to form a part of the orbit 

 of the eyes, and the feptum varium. 



The os fphenoides, or wedge-like bone, which is fo 

 called from its fituation in the middle of the bones of 

 the cranium and face, is of a very irregular figure, and 

 bears fome refemblance to a bat, with its wings ex- 

 tended. This bone is generally divided into a body, 

 and two fides or wings. When we view the external 

 part of the os fphenoides, two or three remarkable pro- 

 ceffes from each fide of it may be obferved, which are 

 all of them again fubdivided. The firft piir confifts of 

 the two large lateral proceffes or wings ; the upper 

 part of each of which is called the temporal procels, 

 becaufe they join with the temporal bones in forming 

 the temples : that part of the wings which projects to- 

 wards ihe infide, fomewhat lower lhan the temporal 

 proceffes, and is fmooth and hollowed, forms part of 

 the orbits. The loweft and back part of each wing 

 runs out with a iharp point, called the fpinous procefs, 

 to meet the point of the pars petrofa of the temporal 

 bone. The fecond pair of external proceffes of the 

 fphenoid bone are the aliform or pterygoid, and which 

 ftand out almoft perpendicular to the bafe of the fkull. 

 Each of them has two plates and a middle foffaat the 

 pofterior furface. Of thefe plates, the exterior is the 

 -broadeftj the interior are longed, and terminate in a 

 hook-like procefs. Another pair of proceffes may be 

 mentioned, viz. the little triangular thin proceffes which 

 come from each fide of the fphenoid bone, where the 



pterygoid 



