INTERNAL BASE OF THE SKULL. 



69 



The anterior fossa, formed by the orbital plates of the frontal bone, the 

 cribriform plate of the ethmoid, and the small wings and part of the body of the 

 sphenoid, supports the frontal lobes of the cerebrum. It is convex laterally above 

 the orbits, but sinks into a hollow over the cribriform plate of the ethmoid, in the 

 middle line of which the crista galli stands up, separating the deep olfactory grooves 

 for the reception of the olfactory bulbs. In front of the crista galli is the foramen 



23 



Fig. 71. SAGITTAL SECTION OF THE ADULT SKULL A LITTLE TO THE LEFT OF THE MEDIAN PLANE. 



(Allen Thomson.) J 



1, nasal bone ; 2, perpendicular plate of the ethmoid with olfactory foramina and grooves at its 

 upper part ; 3, vomer ; 4, right superior maxillary bone, forming part of the wall of the right nasal 

 fossa ; below this is the anterior extremity of the right inferior turbinate bone overhanging x , which 

 is the right inferior meatus of the nose ; 5, crista galli ; 6, inner surface of the frontal bone ; 7, of the 

 parietal bone ; 8, sqnamous part of the temporal ; 9, on the occipital bone below the internal occipital 

 protuberance ; 10, external occipital protuberance ; 11, on the condylar process below the anterior con- 

 ilylar foramen ; 12, on the posterior surface of the petrous below the internal auditory meatus ; between 

 and 12, the groove of the right lateral sinus ; 13, placed above the sella turcica ; 14, left frontal 

 sinus ; 15, left sphenoidal sinus, the figure being placed on the sphenoidal septum ; 16, hard palate 

 and alveolar arch the figure is placed near the lower opening of the posterior palatine canal, and the 

 grooves which extend forwards from it ; 17, anterior nasal spine ; 18, section of the left superior 

 maxillary bone, and near the place to which the line points, the section of the anterior palatine fossa ; 

 19, on the inner surface of the ramus of the lower jaw, below the sigmoid notch, and above the inferior 

 dental foramen ; 20, inner surface of the body of the jaw on the mylo-hyoid ridge ; 21, surface of section 

 of the lower jaw to the left of the sympbysis ; behind the symphysis, and between 21 and 22, the mental 

 spines ; 23, mylo-hyoid groove. 



csecum ; on each side are the numerous apertures of the cribriform plate, the inner 

 openings of the internal orbital canals, and the foramen by which the nasal nerve 

 passes into the nose. 



The foramen caecum sometimes conveys a vein passing from the nose to the superior longi- 

 tudinal sinus. The apertures of the cribriform plate are occupied by the olfactory nerve 

 filaments. Through the anterior internal orbital canal the nasal nerve and the anterior 

 ethmoidal artery enter the skull, and through the posterior, which is less constant, the 

 posterior ethmoidal artery. The foramen, for the exit of the nasal nerve is at the front 



