538 NERVOUS SYSTEM. 



CHAPTER XVII. 



SPIRAL AXD CRANIAL NERVES. 



Spinal nerves Cranial nerves Anatomical classification Physiological classification Motor oculi cora- 

 munis (third nerve) Physiological anatomy Properties and uses Influence upon the movements of 

 the iris Patheticus, or trochlearis (fourth nerve) Physiological anatomy Properties and uses Motor 

 oculi externus, or abducens (sixth nerve) Physiological anatomy Properties and uses Nerve of mas- 

 tication (the small, or motor root of the fifth) Physiological anatomy Properties and uses Facial, 

 or nerve of expression (seventh nerve) Physiological Anatomy Intermediary nerve of \Vrisberg 

 Alternate paralysis General properties Uses of the chorda tympani Influence of various branches 

 of the facial upon the movements of the palate and uvula Spinal accessory (eleventh nerve) Physio- 

 logical anatomy Uses of the internal branch from the spinal accessory to the pneumogastric Influ- 

 ence of the spinal accessory upon the heart Uses of the external, or muscular branch of the spinal 

 accessory Sublingual, or hypoglossal (twelfth nerve) Physiological anatomy Properties and uses 

 Trifacial, or trigeminal (fifth nerve) Physiological anatomy Properties and uses Pneumogastric 

 (tenth nerve) Physiological anatomy Properties and uses General properties of the roots Prop- 

 erties and uses of the auricular nerves Properties and uses of the pharyngeal nerves Properties 

 and uses of the superior laryngeal nerves Properties and uses of the inferior, or recurrent laryngeal 

 nerves Properties and uses of the cardiac nerves Depressor-nerve of the circulation Properties and 

 uses of the pulmonary nerves Properties and uses of the oesophageal nerves Properties and uses of 

 the abdominal nerves. 



WITH a knowledge of the general properties of the nerves belonging to the 

 cerebro-spinal system, it is easy to understand the uses of most of the speck 

 nerves, simply from their anatomical relations. This is especially true of 

 the spinal nerves. These, in general terms, are distributed to the muscles of 

 the trunk and extremities, to the sphincters and the integument covering these 

 parts, the posterior segment of the head, and to certain mucous membranes. 

 It is evident, therefore, that an account of the exact office of each nervoi 

 branch would necessitate a full description, not only of the nerves, but of the 

 muscles of the body, which is manifestly within the scope only of treatises 

 on descriptive anatomy. 



SPINAL NERVES. 



There are thirty-one pairs of spinal nerves ; eight cervical, twelve dorsal, 

 five lumbar, five sacral and one coccygeal. Each nerve arises from the spinal 

 cord by an anterior (motor) and a posterior (sensory) root, the posterior roots 

 being the larger and each having a ganglion. Immediately beyond the 

 ganglion, the two roots unite into a single mixed nerve, which passes out of 

 the spinal canal by the intervertebral foramen. The nerve thus constituted 

 is possessed of motor and sensory properties. It divides outside of the spinal 

 canal into two branches, anterior and posterior, both containing motor and 

 sensory filaments, which are distributed respectively to the anterior and the pos- 

 terior parts of the body. The anterior branches are the larger, and they sup- 

 ply the limbs and all parts in front of the spinal column. 



The anterior branches of the upper four cervical nerves form the cervical 

 plexus, and the four inferior cervical nerves, with the first dorsal, form the 

 brachial plexus. The anterior branches of the dorsal nerves, with the excep- 

 tion of the first, supply the walls of the chest and abdomen. These nerves 

 go directly to their distribution and do not first form a plexus. The ante- 

 rior branches of the upper four lumbar nerves form the lumbar plexus. The 

 anterior branch of the fifth lumbar nerve and a branch from the fourth 



