656 MEDULLA OB LONG ATA AND THE CRANIAL NERVES 



12. The hypoglossal nerve emerges from the furrow between the 

 anterior pyramid and olivary body of the medulla. Its deep origin 

 is formed by a nucleus situated in the floor of the fourth ventricle. 

 A commissure unites the nuclei in the two halves, and each nucleus 

 receives fibers from the opposite cerebral hemisphere. It is a motor 

 nerve and innervates the muscles of the tongue, inclusive of the muse, 

 geniohyoideus and thyreohyoideus. 



