AURICULAR NERVE SPINAL NERVES. 403 



nerve just as it is about to enter the dental foramen. This branch 

 pierces the insertion. of the internal lateral ligament, and descends 

 along a groove in the bone to the superior surface of the mylo-hyoid 

 muscle, to which it is distributed. 



The ANTERIOR AURICULAR NERVE passes directly backwards be- 

 hind the articulation of the lower jaw, against which it rests. In 

 this situation it divides into two branches, which reunite, and form 

 a kind of plexus. From the plexus two branches are given off 

 ascending and descending. The ascending or temporal branch* 

 sends a considerable branch of communication to the facial nerve, 

 and then ascends in front of the ear to the temporal region, upon 

 which it is distributed in company with the branches of the temporal 

 artery. In its course it sends filaments to the temporo-maxillary 

 articulation, to the pinna and meatus of the ear, and to the integu- 

 ment in the temporal region. It communicates on the temple with 

 branches of the facial, supra-orbital, lachrymal, and temporo-malar 

 nerve. The descending branch enters the parotid gland, to which 

 it sends numerous branches; it communicates with the inferior 

 dental and auricularis magnus nerve, and supplies the external ear 

 and the temporo-maxillary articulation. t 



SPINAL NERVES.. 



There are thirty-one pairs of spinal nerves, each arising by two 

 roots, an anterior or motor root, and a posterior or sensitive root. 



The anterior roots arise from a narrow white line upon the ante- 

 rior columns of the spinal cord, and gradually approach towards the 

 anterior longitudinal sulcus as they descend. 



The posterior roots, more regular than the anterior, arise from a 

 narrow gray band formed by the internal gray substance of the 

 cord. They are larger, and the filaments of the origin more nume- 

 rous than those of the anterior roots. A ganglion is found upon 

 each of the posterior roots in the intervertebral foramina. The 

 first cervical nerve forms an exception to these characters. Its 

 posterior root is smaller than the anterior; there is frequently 

 no ganglion upon it, and it often joins in the whole or in part with 

 the spinal accessory nerve. 



After the formation of the ganglion the two roots unite, and con- 

 stitute a spinal nerve, which escapes through the intervertebral fora- 

 men, and divides into an anterior branch, for the supply of the front 

 half of the body, and a posterior branch, for the posterior half. 



The anterior branches, with the exception of the two first cervical 

 nerves, are larger than the posterior; an arrangement which is 

 proportioned to the larger extent of surface they are required to 

 supply. 



* This is usually called the superficial temporal nerve. G. 



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