I50 



A MANUAL OF ANATOMY 



Fig. 85. — Sagittal Section of the Skull to the Right of the Median 



Plane. 



F, Frontal ; P, Parietal ; O, Occipital ; T, Temporal. 



22. Anterior Nasal Spine 



23. Inferior Turbinate Bone 



24. Middle Meatus 



25. Inferior Turbinate Process 

 of Ethmoid 



26. Infundibulum 



27. Nasal Bone 



28. Right Sphenoidal Sinus 



29. Right Frontal Sinus 



30. Crista Galli 



31. Optic Foramen 



32. Pterion 



The Internal Base of the Skull. 



The internal base forms the floor of the cranial cavity, and is of 

 very irregular outline and thickness. The thickest and densest 

 parts are the petrous portions of the temporals. The mastoid 

 portion of the temporal and the basilar part of the occipital are also 

 thick. The thinnest parts are the cribriform plate of the ethmoid 

 and the orbital plates of the frontal, but the central portions of the 

 cerebellar fossae of the occipital are also thin, sometimes remarkably 

 so. The interior of the base is divided into three fossae — anterior, 

 middle, and posterior. 



Anterior Fossa. — The floor of this fossa is formed by the orbital 



