HTPOGLOSSAL NERVE. 389 



ments from the cavernous plexus, and one from the ophthalmic 

 nerve. 



6th pair, ABDUCENTES. The abducens nerve arises from the upper 

 part of the corpus pyramidale, close to the pons Varolii, several of 

 its filaments of origin passing between the fasciculi of the pons. It 

 pierces the dura mater upon the basilar process of the sphenoid 

 bone, and ascends to the cavernous sinus. It then runs forward along 

 the inner wall of the sinus, below the other nerves ; and, resting 

 against the internal carotid artery, passes between the two heads of 

 the external rectus, and is distributed to that muscle. As it enters 

 the orbit it lies upon the ophthalmic vein, from which it is separated 

 by a lamina of dura mater. In the cavernous sinus it is joined by 

 two filaments from the carotid plexus, and by one from the ophthal- 

 mic nerve. Mr. Mayo has traced the origin of this nerve between 

 the fasciculi of the corpora pyramidalia to the posterior part of the 

 medulla oblongata ; and Mr. Grainger has pointed out its connexion 

 with the gray substance of the spinal cord. 



9th pair, HYPOGLOSSAL (lingual). The ninth nerve, the true mo- 

 tor nerve of the tongue, arises by eight or ten filaments from the 

 side of the corpus pyramidale of the medulla oblongata. These 

 filaments are disposed in two fasciculi which unite into a single 

 nerve at the posterior condyloid foramen. The lingual nerve then 

 passes forward between the internal carotid artery and internal 

 jugular vein, and descends along the anterior and inner side of the 

 vein to a point parallel with the angle of the lower jaw. It next 

 curves inwards around the occipital artery, with which it forms a 

 loop, and crosses the lower part of the hyo-glossus, muscle to the 

 genio-hyo-glossus, in which it terminates by sending filaments on- 

 wards with the anterior fibres of this muscle^ as far as the tip of the 

 tongue. It is distributed to the muscles of the tongue, and princi- 

 pally to the genio-hyo-glossus. While resting on the hyo-glossus 

 muscle it has a flattened appearance, and communicates beneath the 

 mylo-hyoideus of the gustatory nerve. 



The Branches of the hypoglossal nerve are : 



Communicating branches with the Pneumogastric, 



Spinal accessory, 

 First and second cervical 



Sympathetic. 

 Descendens noni, 

 Hyoidean branch, 

 Communicating filaments with the gustatory nerve. 



The Communications with the pneumogastric and spinal acces- 

 sory take place through the medium of a plexiform interlacement of 

 branches at the base of the skull, behind the internal jugular vein. 

 The communications with the sympathetic nerve are derived from 

 the superior cervical ganglion. 



