126 



THE INTERNAL BASIS OF THE CRANIUM. 



The Internal Basis of the Cranium 



Is much more important. It is divided into three fossae on each 

 side ; the anterior of these are most superficial, and the posterior 

 the deepest. The bottoms of the anterior foss& are formed by 

 the orbitar processes of the osfrontis, and consequently are con- 

 vex ; between them is the cribriform plate of the ethmoid, which 

 is commonly sunk below the adjoining surface. The crista galli 

 is very conspicuous ; and the foramen caecum can almost always 

 be seen. The crista galli is evidently the beginning of the pro- 

 minent ridge, which continues on the os frontis, and supports the 

 falx of the dura rnater. The posterior margins of these fossae 

 are formed by the lesser wings of the sphenoid bone. 



The middle fossa are formed by the great wings of the 

 sphenoidal bone, and by the squamous and petrous portions 

 of the temporal bone. They are lower than the anterior, 

 and higher than the posterior fossae. The projection of the 

 Fig. 30.* margin of the anterior fossae 



into these cavities, corresponds 

 with the separation between 

 the anterior and middle lobes 

 of the brain. The suture be- 

 tween the sphenoidal and tem- 

 poral bones is evident in these 

 fossae. The upper surface of 

 the body of the sphenoid bone, 

 or the sella turcica is between 

 them ; and all the peculiarities 

 of its surface are very conspi- 

 cuous. The first five foramina 

 of the sphenoidal bone can IK- 

 easily ascertained, and also, the 

 anterior foramen lacerurn and 



* The cerebral surface of the base of the skull. 1. One side of the anterior 

 fossa j the number is placed on the roof of the orbit, formed by the orbital plate 

 of the frontal bone. 2. The lesser wing of the sphenoid. 3. The crista galli. 

 4. The foramen caecum. 5. The cribriform lamella of the ethmoid. 6. The 

 processus olivaris. 7. The foramen opticum. 8. The anterior clinoid process. 

 9. The carotid groove upon the side of the sella Turcica, for the internal carotid 

 artery and cavernous sinus. 10, 11, 12. The middle fossa of the base of the 

 skull. 10. Marks the great ala of the sphenoid. 11. The squamous portion of 



