SPINAL NERVES. 319 



foramen, through which it passes to the upper inner part 

 of the sterno-mastoid muscle, which it pierces, and is 

 finally distributed to the trapezius. Its branches are 

 communicating 1 with glosso-pharyngeal, pneumogastric, 

 and cervical nerves, and muscular branches to the 

 sterno-mastoid and trapezius. 



12. HYPOGLOSSAL NERVE. Is the motor nerve of the 

 tongue. It arises in the groove between the anterior 

 pyramid and olivary body, above the plane of the pneu- 

 mogastric. Its fibres of origin are numerous. The 

 nerve passes through the anterior condyloid or hypoglos- 

 sal foramen, descends deeply in the neck, and is distrib- 

 uted to the tongue-muscles. It sends off branches of 

 communication to the pneumogastric, cervical, and sym- 

 pathetic nerves, and a descending branch (the descendens 

 noni), \vhich forms a loop, on the anterior part of the 

 sheath of the cervical vessels, with the communicans 

 noni, formed by branches from the second and third cer- 

 vical. From this loop branches pass to the sterno-hyoid, 

 sterno-thyroid, and omo-hyoid muscles. 



SPINAL NERVES. 



There are 31 pairs of nerves that arise from the sides 

 of the spinal cord. They are arranged in five regions : 



Cervical, 8 pairs. 



Dorsal, 12 " 



Lumbar, 5 " 



Sacral, 5 " 



Coccygeal, 1 pair. 



They arise by two roots, an anterior or motor, from 

 the antero-lateral fissure, and a posterior or sensory or 

 ganglionic, from the postero-lateral fissure. The anterior 

 roots are the smaller. The posterior or larger has a 

 ganglion on it. The two roots unite in or near the 



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