THE SIXTH OR ABDUCENT NERVE 



683 



and i>;iiip;ival l)ranchos dotached from the nerve within the mandi})le are arranged 

 Hke the corresponcUng nerves of the upper jaw. 



7. The lingual nerve (N. linguahs) arises by a eommon trunk with the inferior 

 alveolar or dental nerv(> (l*'igs. 436, 437). After separating from the latter it runs 

 downward and forward, lying at first between the ramus of the mandible and the 

 internal pterygoid muscle, then on the inner face of the mylo-hyoid. On n^aching 

 the root of the tongue it divides into superficial and deep l)ranches. The super- 

 ficial branch (Ramus superficialis) runs forward on the stylo-glossus and accom- 

 panies the submaxillary duct on the deep face of the sublingual gland. It supplies 

 the mucous membrane of the tongue and the floor of the mouth. At the root of the 

 tongue it gives off a recurrent branch to the isthmus faucium, which connnunicates 

 with the lingual branch of the glosso-pharyngeal nerve. The larger deep branch 

 (Ramus profundus) turns around the lower edge of the hyo-glossus, passes upward 

 and forward between that muscle and the genio-glossus, and continues forward on 

 the latter to the tip of the tongue. It gives branches to the mucous membrane and 

 the fungiform papillffi of the tongue, and anastomoses with branches of the hypo- 



& 



-"-V- 





Fig. 516. — Part op Branch of Lower Jaw op Horse, Internal View. 

 The bone ha.s been removed to show the vessels and nerves, i, 1' , Inferior alveolar or dental nerve; 2, 2. 

 branches to cheek teeth and gunxs; 2' , branch to canine and incisor teeth; 3, 3', inferior alveolar or dental artery; 

 4, satellite vein. (After Leisering's Atlas.) 



glossal nerve and with the superficial branch. Minute ganglia occur on the finer 

 branches of the lingual nerve. The chorda tympani branch of the facial joins the 

 lingual nerve at the origin of the latter and is incorporated with it in its distribution 

 to the tongue. 



THE SIXTH OR ABDUCENT NERVE 



The abducent nerve (N. abducens) emerges from the brain behind the pons 

 and just external to the pyramid (Fig. 499). It passes forward across the pons, 

 pierces the dura mater, and accompanies the third and ophthahnic nerves, below 

 which it emerges through the foramen lacerum orbitale. In the orbit it divides 

 into two branches; the larger of these enters the external rectus, the smaller sup- 

 plies the superior and external parts of the retractor muscle of the eyeball. Within 

 the cranium it receives filaments from the carotid plexus of the sympathetic. 



The fibers of the abducent nerve are axones of the large muhipolar cells of the abducent 

 nucleus which is situated beneath the eminentia teres of the floor of the fourth ventricle. The 

 nucleus lies within the loop formed by the fibers of orijiin of the facial nerve. It is connected 

 with (a) the anterior olive; (6) the oculomotor nucleus of the opposite side; (c) the motor area of 

 the cerebral cortex by means of the pyramidal tract of the opposite side. 



