ANATOMY AND PHYSIOLOGY OF THE BRAIN 379 



part to the vagus. The latter part arises as five or 

 six filaments from the lateral tract of the medulla, 

 below the origin of the vagus. 



The spinal portion arises from the lateral column 

 of the cord as low as the sixth cervical nerve, the 

 fibers being connected with the anterior horn of gray 

 matter. This part then ascends, between the posterior 

 nerve roots and the ligamentum denticulatum, through 

 the foramen magnum, then out again by the jugular 

 foramen, lying in the sheath of the vagus, and here 

 communicates with the accessory portion. After 

 its exit from the skull it crosses the internal jugular 

 vein and pierces the sternomastoid to end in the 

 trapezius muscle. 



THE HYPOGLOSSAL. The twelfth, or hypoglossal, 

 nerve arises by ten to fifteen filaments from the groove 

 between the pyramid and olivary body in the medulla. 

 The deep origin is from a nucleus in the floor of the 

 fourth ventricle. The filaments form two bundles 

 which pierce the dura separately and unite in the 

 anterior condylar foramen. The nerve descends behind 

 the internal carotid artery and internal jugular vein, 

 closely bound to the vagus. 1 



The Spinal Nerves. The spinal nerves consist, on each 

 side, of eight cervical, twelve thoracic, five lumbar, 

 five sacral, and one coccygeal, in all thirty-one pairs, 

 which arise from the cord by two roots, anterior and 

 posterior. The latter are the larger, and are supplied 

 with ganglia. The suboccipital or first cervical nerve 

 has no ganglion. The two roots unite just beyond 

 the ganglion, and the resulting trunk divides into two 

 divisions, anterior and posterior, each containing 

 fibers from both roots, sensor and motor. The posterior 

 division divides into an external and an internal branch. 

 The anterior divisions in the dorsal region remain 

 separate, but elsewhere they unite into plexuses. 



1 See Fig. 131 for origin of spinal nerves. 



