SYMPATHETIC NEKVOUS SYSTEM. 835 



11. The Spinal-Accessory Nerve. — This nerve arises by two 

 separate roots, one from the accessory nucleus of the medulla, which is 

 connected with the nucleus of the vagus, the other between the anterior 

 and posterior roots of the spinal nerves, as far down as the fifth cervical 

 nerve, its fibres in the cord having been traced to a nucleus on the outer 

 side of the anterior cornua. The anterior branch passes entirely into 

 the vagus and gives to it most of its motor fibres and all the cardio- 

 inhibitory fibres. The spinal-accessory is the motor nerve to the sterno- 

 mastoid and trapezius muscles ; it receives sensory branches from the 

 cervical nerves. 



12. The Hypoglossal Nerve. — The hypoglossal nerve arises from 

 two large-celled nuclei in the calamus scriptorius and one adjoining 

 small-celled nucleus, being connected both with the olivary body and 

 the brain. It is the motor nerve for the muscles of the tongue and most 

 of the hyoid muscles. It receives afferent fibres from the fifth and tenth 

 nerves and vaso-motor fibres from the sympathetic. 



VIII. THE SYMPATHETIC NERVOUS SYSTEM. 



The great sympathetic nerve, constituted by a ganglionic chain, 

 composed of a series of ganglia connected by nerve-fibres, is located on 

 each side of the vertebral column. Three different forms of structure 

 may be recognized in this portion of the nervous system — the ganglia, 

 the peripheral branches, and the connecting filaments. The two chains 

 situated on each side of the median line are connected by transverse 

 fibres, giving off numerous branches, which anastomose among themselves 

 and form plexuses (Fig. 362). 



The sympathetic nerve may be divided into three divisions. In the 

 cephalic portion are found the ophthalmic, the sphenopalatine, the otic, 

 the submaxillary, and the sublingual, with the three cervical ganglia. In 

 the thorax and abdomen are found the other two divisions, which like- 

 wise consist of a number of ganglia united together by anastomosing 

 filaments. 



The ganglia consist of gray substance united with nerve-tubules. 



The fibres are non-medullated and connect the ganglia. Each spinal 

 nerve forms connections with adjacent sympathetic ganglia by means of 

 the rami communicantes, which are formed by nerve-fibres coming from 

 both the anterior and the posterior roots of the spinal nerves. In addi- 

 tion to the non-medullated fibres entering into the constitution of the great 

 sympathetic nerve are also fine nerve-tubules, which in their structure 

 are analogous to those of the cerebro-spinal axis. Such filaments are 

 much less abundant than the gray or non-medullated fibres of Remak. 



The functions of the sympathetic nervous system have already been 



