TNEUMOGASTRIC NERVE. 573 



the most varied uses. Arising from the medulla oblongata by a purely senso- 

 ry root, it communicates with at least five motor nerves, and it is distributed 

 largely to muscular tissue, both of the voluntary and the involuntary variety. 



Physiological Anatomy. The apparent origin of the pneumogastric is 

 from the lateral portion of the medulla oblongata, 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 pneumogas- 

 tric, in 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 ap- 

 pear to be in the main identical. Tracing the filaments from without in- 

 ward, they may be followed in four directions : (1) The anterior filaments 

 pass from without inward, first very superficially, in the direction 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 posterior filaments are 

 superficial, and they pass, with the fibres of the restiform body, toward the 

 cerebellum. (3) Of the intermediate filaments, the anterior pass through 

 the restiform body, the greatest number extending to the median line, in 

 che floor of the fourth ventricle. A few fibres are lost in the middle fascic- 

 uli of the medulla and a few pass toward the brain. (4) The posterior 

 intermediate filaments traverse the restiform body, to the floor of the fourth 

 ventricle, when some pass to the median line, and others descend in the sub- 

 stance of the medulla. 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 pneumogastric. 

 In the jugular foramen, is a well marked, grayish, ovoid enlargement, one- 

 sixth to one-fourth of an inch (4-2 to 6*4 mm.) in length, called the jugular 

 ganglion, or the ganglion of the root. This is united by two or three fila- 

 ments with the ganglion of the glosso-pharyngeal. It is a true ganglion, 

 containing nerve-cells. After the nerve has emerged from the cranial cav- 

 ity, it presents on its trunk another grayish enlargement, half an inch to an 

 inch (12 to 25 mm.) in length, called the ganglion of the trunk. This has 

 a plexiform structure, the white fibres being mixed with grayish fibres and 

 nerve-cells. The exit of the nerve from the cranial cavity is by the jugular 

 foramen, or posterior foramen lacerum, in company with the spinal acces- 

 sory, the glosso-pharyngeal nerve and the internal jugular vein. 



Anastomoses. There are occasional filaments of communication which 

 pass from the spinal accessory to the ganglion of the root of the pneumogas- 

 tric, but these are not constant. After both nerves have emerged from the 

 cranial cavity, an important branch of considerable size passes from the spi- 

 nal accessory to the pneumogastric, with which it becomes closely united. 

 Experiments have shown that these filaments from the spinal accessory pass 

 in great part to the larynx, by the inferior laryngeal nerves. 



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