Cranial Nerves. 



123 



467. The Cranial Nerves at the Base of the Skull. 



2 / 3 natural size. 



The first of the twelve pairs of cranial nerves is the 

 olfactory, Nervus olfactorius. It arises at the under surface of the 

 anterior lobe from the Trigonum olfactorium as a flat, prismoid band, 

 Tractus olfactorius, passes forwards in a deep groove on the under surface 

 of the anterior lobe, converging with that of the opposite side ; on 

 reaching the cribriform plate of the ethmoid bone it expands into a 

 mass of greyish- white substance, the olfactory bulb, Bulbus olfactorius. 

 From the under part of this bulb are given off two rows of filaments, 

 about 20 in number, which pass through the cribriform foramina to the 

 upper part of the mucous membrane of the nose. Here they form a 

 network at the Septum narium and inner surfaces of the ethmoidal tur- 

 binated bones, from which very small filaments ascend to the mucous 

 membrane. This network reaches down furthest at the Septum narium 

 (see Fig. 293), at the ethmoidal labyrinth only down to the lower border 

 of the middle turbinated bone. 



Heitzmann, Atlas. II. 17 



