530 NERVOUS SYSTEM 



there is no alteration in the nutrition of the organs of special sense ; but 

 in this respect the facts in regard to the seat of the lesion are not so 

 satisfactory as in experiments on the lower animals, it being difficult to 

 limit exactly the boundaries of the lesion. 



PNEUMOGASTRIC (TENTH NERVE) 



Of all the cranial nerves, the pneumogastric presents the greatest 

 number of anastomoses, the most remarkable course and the most varied 

 uses. Arising from the bulb by a purely sensory root, it communicates 

 with at least five motor nerves and is distributed largely to muscular 

 tissue, both of the voluntary and the involuntary variety. On account 

 of its wide distribution and wandering course, it is often called the vagus 

 or par vagum. 



Physiological Anatomy. The apparent origin of the pneumogastric 

 is from the lateral portion of the bulb, just behind the olivary body, 

 between the roots of the glosso-pharyngeal and the spinal accessory. 

 The deep origin is mainly from what is called the nucleus of the pneu- 

 mogastric, at the inferior portion of the gray substance in the floor of 

 the fourth ventricle. The course of the fibres, traced from without 

 inward, is somewhat intricate. 



The deep origins of the pneumogastric and glosso-pharyngeal nerves 

 appear to be in the main identical. Tracing the filaments from without 

 inward, they may be followed in four directions: (i) The anterior 

 filaments pass from without inward, first very superficially, in the direc- 

 tion of the olivary body ; but they then turn and pass deeply into the 

 substance of the restiform body, in which they are lost. (2) The pos- 

 terior filaments are superficial, and they pass, with the fibres of the resti- 

 form body, toward the cerebellum. (3) Of the intermediate filaments, 

 the anterior pass through the restiform body, the greatest number extend- 

 ing to the median line, in the floor of the fourth ventricle. A few fibres 

 are lost in the middle fasciculi of the bulb and a few pass toward the brain. 

 (4) The posterior intermediate filaments traverse the restiform body to 

 the floor of the fourth ventricle, where some pass to the median line and 

 others descend in the substance of the bulb. It is difficult to follow the 

 fibres of origin of the pneumogastrics beyond the median line ; but 

 recent observations leave no doubt of the fact that many of these fibres 

 decussate in the floor of the fourth ventricle. 



There are two ganglionic enlargements belonging to the pneumo- 

 gastric. In the. jugular foramen, is a well-marked, grayish, ovoid en- 

 largement, one-sixth to one-fourth of an inch (4.2 to 6.4 millimeters) in 

 length, called the jugular ganglion, or the ganglion of the root. This 



