514 



THE CRANIAL NERVES. 



lobe, near the median line, and terminating anteriorly in a flattened 

 ovoid mass of gray substance, the "olfactory bulb." The olfactory 

 bulb rests upon the cribriform plate of the ethmoid bone, and gives off, 

 through the perforations in this bone, the true nervous filaments sup- 

 plying the olfactory membrane in the nasal passages. The prismatic 

 tract which connects the olfactory bulb with the rest of the brain is in 

 reality, according to both Henle and Meynert, a prolongation of one of 

 the cerebral convolutions. It originates in a rounded eminence called 

 the " olfactory tubercle," situated at the back part and under surface 

 of the anterior cerebral lobe, just inside the island of Reil, with which it 

 is connected. It consists, like the other cerebral convolutions, of gray 

 substance containing pyramidal cells. Its peculiarity, as shown by 

 Henle, consists in the fact that bundles of nerve fibres from the interior 



Fig. 169. 



Cba 



LiOXGITTTDINAL SECTION OF THE CEREBRAL HEMISPHERE, through the Situa- 

 tion of the olfactory tubercle and part of the olfactory nerve. 1. Olfactory nerve. 2. Olfac- 

 tory tubercle. Cs. Corpus striatum. Coa. Anterior cerebral com'missure. Cba. Anterior 

 commissure of the base of the brain. Magnified once and one half. (Henle.) 



pass through its cortical layer of gray matter, and appear upon its 

 surface as more or less distinct striations of white substance. It is 

 these white striations which have been designated as the olfactory 

 "roots," and which give to the tract terminating in the bulb the external 

 appearance of a nerve. They are derived from the white substance of 

 the cerebral hemispheres, and continue forward to the gray matter of 

 the olfactory bulb. A communication is established between the olfac- 

 tory nerves of the two opposite sides through the internal white sub- 

 stance of the olfactory tubercles. According to Yulpian, there is also 

 a more direct communication, visible in the dog, the sheep, and the 



