ANATOMY OF THE NERVOUS SYSTEM. 175 



cord, between the anterior and posterior roots of the proper 

 cervical spinal nerves. Each, however, runs into the skull 

 cavity alongside of the spinal cord and, getting a few fila- 

 ments from the medulla oblongata, passes out along with the 

 glossopharyngeal and pneumogastric nerves. Outside the 

 skull it divides into two branches, one of which joins the 

 pneumogastric trunk, while the other is distributed to mus- 

 cles about the shoulder. 



The twelfth pair of cranial nerves (liypoglossi), XII, arise 

 from the sides of the medulla oblongata; they are distributed 

 mainly to the muscles of the tongue and hyoid bone. 



Deep Origins of the Cranial Nerves. The places referred 

 to above, at which the various cranial nerves appear on the 

 surface of the brain, are known as their superficial origins. 

 From them the nerves can be traced for a lesser or greater way 

 in the substance of the brain until each is followed to one or 

 more masses of gray matter, which constitute its proper start- 

 ing-point and are known as its deep origin. The deep origins 

 of all except the first and second and part of the eleventh lie 

 in the medulla oblongata, midbrain, and thalamen cephalon. 



The Ganglia and Communications of the Cranial Nerves. 

 Besides the Gasserian ganglion above referred to, many others 

 are found in connection with the cranial nerves. Thus for 

 example there is one on each of the main divisions of the 

 trigeminal, two are found on each pneumogastric and two in 

 connection with the glossopharyngeal. At these ganglia and 

 elsewhere, the various nerves often receive branches from 

 neighboring cranial or spinal nerves, so that very soon after 

 it leaves the brain hardly any, except the olfactory, optic, and 

 auditory, remains free from fibres derived from other trunks. 

 This often makes it difficult to say from where the nervej of 

 a special part have come; for example, the nerve-fibres going 

 to the submaxillary salivary gland from the trigeminal leave 

 the brain first in the facial and only afterwards enter the 

 fifth; and many of the fibres going apparently from the 

 pneumogastric to the heart come originally from the spinal 

 accessory. 



The Sympathetic System. The ganglia which form the 

 main centres of the sympathetic nervous system lie in two 

 rows (s, Fig. 2, and sy, Fig. 3), one on either side of the 

 bodies of the vertebrae. Each ganglion is united by a nerve- 

 .trunk with the one in front of it, and so two great chains are 



