THE HYPOGLOSSAL NERVE 105 



motor in function. It arises from a nucleus which is situated 

 in the dorsal part of the medulla oblongata (Fig. 52) and which 

 is continuous below with the anterior column of grey matter 

 in the spinal medulla. The fibres pass forwards through the 

 substance of the medulla oblongata and come into close 

 relationship with the pyramidal tract, before they emerge 

 from the groove between the pyramid and the olive (Fig. 8). 

 As it runs laterally from the medulla oblongata, the hypo- 

 glossal nerve lies below the ninth, tenth and eleventh nerves 

 in the posterior cranial fossa. It passes through the hypo- 



FIG. 52. Section through Upper Part of Medulla Oblongata. 

 i. Pyramidal tract. 2. Olivary nucleus. 7. Nucleus of hypoglossal nerve. 



glossal canal (anterior condyloid foramen), which pierces the 

 occipital bone just above the condyle. Consequently, after 

 leaving the skull, the nerve descends close to the lateral 

 aspect of the atlanto-occipital joint. On this account, it may 

 be involved in tuberculous disease of the articulation, and 

 paralysis and atrophy of one half of the tongue is a valuable 

 localising symptom in cervical caries. 



In its extra-cranial course^ the hypoglossal nerve is at first 

 related to the ninth, tenth and eleventh nerves, but it passes 

 forwards on a level with the greater cornu of the hyoid bone 

 to reach the tongue. 



