HYPOGLOSSAL NERVE. 



793 



G.Ph. 



the lateral aspect of the spinal medulla, between the anterior and posterior roots 

 of the spinal nerves, its origin extending from the level of the accessory portion 

 as low as the origin of the sixth cervical nerve (for the deep origin, see p. 596). 

 Successively joining together, the fila radicularia (rootlets) form a trunk which 

 ascends in the subdural space of the spinal medulla, posterior to the ligamenturn 

 denticulatum, to the foramen magnum. There the two portions unite into a single 

 trunk, which leaves the cranial cavity through the jugular foramen in the same 

 compartment of dura mater as the vagus nerve 

 (Fig. 647, p. 771). 



Ramus Inter mis. In the jugular foramen 

 the accessory portion of the nerve or internal 

 ramus (after furnishing a small branch to the 

 jugular ganglion of the vagus) applies itself to 

 the ganglion nodosum, and in part joins the 

 ganglion, in part the trunk of the nerve beyond 

 the ganglion. By means of these connexions 

 the vagus receives viscero- motor and cardio- 

 inhibitory fibres. 



Ramus Externus. The spinal portion of the 

 nerve, or external ramus, extends into the neck, 

 where at first it lies along with other nerves, in 

 the interval between the internal carotid artery 

 and the internal jugular vein. Passing obliquely 

 downwards and laterally over the vein, it de- 

 scends close beneath the sterno-mastoid muscle, 

 which it supplies as it pierces it on its deep 

 surface. After crossing the posterior triangle 

 the nerve ends by supplying the trapezius muscle 

 on its deep surface. This portion of the nerve 

 communicates in three situations with nerves 

 from the cervical plexus (1) in or beneath the 

 sterno-mastoid, with the branch for the muscle 

 derived from the second cervical nerve ; (2) in Flo> 663 ._s CH EME OF THE ORIGIN, CON- 

 the posterior triangle, with branches from the NEXIONS, AND DISTRIBUTION OP THE 

 third and fourth cervical nerves; (3) beneath ACCESSORY NERVE. 



the trapezius, with the branches for the muscle Sp. Ace, Accessory nerve ; C.l-4, First lour 



derived from the third and fourth cervical nerves. cervical nerves (posterior roots) ; Va, 



Vagus nerve ; R, Ganglion jugulare ; T, 

 Ganglion nodosum ; G.Ph, Glossopharyn- 

 geal nerve ; S.M, Nerves to sterno- 

 cleido-mastoid ; Tr, Nerves to trapezius ; 

 F. M, Foramen magnum ; J. F, Jugular 

 foramen. 



S.M. 



NERVUS HYPOGLOSSUS. 



The twelfth or hypoglossal nerve arises by 

 numerous fila radicularia from the front of the 

 medulla oblongata between the pyramid and the olive (Fig. 643, p. 768) (for the 

 deep origin, see p. 594). The fila arrange themselves in two bundles which 

 separately pierce the dura mater, and unite in the hypoglossal canal, or after 

 emerging from the skull. In the neck the nerve arches downwards and forwards 

 towards the hyoid bone, and then turns medially among the supra-hyoid muscles 

 to the tongue. At first it is placed deeply, along with other cerebral nerves, 

 on the lateral side of the internal carotid artery; it then curves forwards and 

 downwards over the two carotid arteries, lying medial to the digastric and stylo-hyoid 

 muscles. As it crosses the external carotid artery it hooks round the occipital artery. 

 Above the greater cornu of the hyoid bone the nerve conceals the lingual artery ; 

 and it then disappears between the mylo-hyoid and hyoglossus muscles to reach 

 the tongue, in the muscular substance of which it terminates. 



Communications. In its course the hypoglossal nerve has the following communica- 

 tions with other nerves : Near the base of the skull it is connected by small branches 

 with (1) the superior cervical ganglion of the sympathetic ; (2) the ganglion nodosum 

 of the vagus ; (3) by a larger branch, with the loop between the first two cervical 

 nerves ; (4) as it crosses the external carotid artery it receives a communication from the 



