276 THE NERVOUS SYSTEM 



bered from before backward in the order in which they pass 

 through the dura mater. Their names, indicating something of 

 their function, and corresponding to their numbers, are as follows: 



I. Olfactory. 

 II. Optic. 



III. Motor Oculi Communis. 



IV. Patheticus (Trochlearis) . 

 V. Trifacial (Trigeminus) . 



VI. Abducens. 

 VII. Facial. 

 VIII. Auditory. 

 IX. Glosso-pharyngeal. 

 X. Pneumogastric (Vagus). 

 XI. Spinal Accessory. 

 XII. Hypoglossal. 



The point at which one of these nerves can be seen to issue 

 from the brain tissue is the apparent origin, while the gray nu- 

 cleus, or nuclei, to which the fibers can be traced in the brain 

 substance is the deep origin. 



First Nerve (Olfactory). 



Origin. This is a nerve of special sense. Its apparent or- 

 igin is by three roots. The internal root issues from the gyrus 

 f ornicatus ; the middle from the under surface of the frontal lobe 

 anterior to the anterior perforated space; the external from the 

 temporo-sphenoidal lobe. These three roots unite to pass for- 

 ward underneath the frontal lobe near the longitudinal fissure 

 as the olfactory tract. The deep origin is unsettled. 



Course and Distribution. Reaching the upper surface of the 

 cribriform plate of the ethmoid, the olfactory tract expands into 

 the olfactory bulb, from the under surface of which are given 

 off the special nerve fibers of the sense of smell. They are about 



