142 HISTOLOGY 



sory. Its large ganglion becomes subdivided into the vestibular ganglion, with fibers 

 to the semicircular ducts or "organ of equilibration," and the spiral ganglion, which 

 sends fibers to the auditory cells of the cochlea. 



The glosso-pharyngeal nerve is chiefly sensory, but it has a small lateral motor 

 root. It has two ganglia, one above the other, the superior ganglion (ganglion superius) 

 and the petrosal ganglion (ganglion petrosum), respectively. The principal branches 

 are the sensory tympanic nerve, which supplies the mucous membrane of the middle 

 ear; the sensory lingual branch, which passes to the back of the tongue and ends in 

 contact with cells of the taste buds, being the nerve of taste; and the mixed pharyngeal 

 branch which is distributed to the pharynx. It supplies the stylo-pharyngeal muscle. 



The vagus nerve, which is sensory, is joined by the accessory nerve, which is motor, 

 so that the vagus is regarded as a mixed nerve. It has two ganglia, the jugular ganglion 

 (ganglion jugulare} above, and the nodose ganglion (ganglion nodosum) below. 

 Its principal branches are the sensory auricular branch, which is distributed to the 

 skin of the external ear; the mixed superior laryngeal nerve, distributed to certain 

 laryngeal muscles and to the mucous membrane of the larynx down to the vocal 

 folds; the recurrent nerve, which terminates as the superior laryngeal in the vocal 

 muscles and mucous membrane of the lower part of the larynx; cardiac branches, 

 which anastomose with the cardiac sympathetic plexus; and finally, from the main 

 trunk of the nerve as it passes through the thorax into the abdomen, branches to 

 the oesophagus, trachea, lungs, stomach, small intestine, liver, spleen and kidneys. 

 Many of these branches anastomose with the sympathetic system. The wide 

 range of this nerve is indicated by the term vagus. 



The accessory nerve is wholly motor, and consists of lateral roots which arise from 

 the hind-brain, and also from the spinal cord as far down as the sixth cervical ganglion. 

 Beginning as a small bundle of fibers underneath the dorsal roots on the side of the 

 spinal cord, it increases in size as it passes upward toward the brain, receiving acces- 

 sions of fibers in its course. It arches toward the vagus and descends in contact 

 with it, finally dividing into external and internal branches. The external ramus 

 supplies the sterno-mastoid muscle and a part of the trapezius; the internal ramus 

 joins the vagus. 



The hypoglossal nerve is made up entirely of ventral roots, and is the motor nerve 

 for the lingual muscles. 



In the head the sympathetic system is intimately associated with the 

 cerebral nerves, along the main branches of which the ganglion cells mi- 

 grate. They accumulate in four ganglia, all of which are associated with 

 the trigeminal nerve. These are the ciliary, spheno-palatine, otic and 

 sub maxillary ganglia (Fig. 128). 



The ciliary ganglion receives its cells from the ophthalmic nerve and in part from 

 the oculomotor nerve, with both of which it remains permanently connected. The 

 sympathetic plexus which ascends around the internal carotid artery also sends fibers 

 to it. Branches from the ciliary ganglion are distributed to the front of the eye, 

 especially to the ciliary muscles and the dilator of the iris. 



The spheno-palatine ganglion derives most of its cells from the maxillary nerve, but 

 it is in communication also with the large superficial petrosal nerve and the sympa- 

 thetic plexus around the internal carotid artery. Some of its fibers reach the orbit, but 

 most of them are distributed to the mucous membrane of the nose and palate. 



The otic and submaxillary ganglia both receive cells from the mandibular nerve, 



