118 ANATOMY IN A NUTSHELL. 



olivary bodies of the medulla. (Plate CLXXXVII). Its deep origin is from 

 the trigonum hypoglossi in the floor of the fourth ventricle. The nerve passes 

 in two bundles through the anterior condyloid foramen after which they unite. 

 It now passes downward hot ween the tenth and eleventh nerves and between the 

 internal carotid artery and the internal jugular vein to the lower border of the 

 Digastric muscle. It now curves round the occipital artery crossing the ex- 

 ternal carotid and lingual arteries to pass between the Mylo-hyoid and Hyo- 

 glossus muscle. It now enters the Genio-hyo-glossus muscle and is continued 

 forward to the tip of the tongue. Its branches of communication are (1) with 

 the GANGLION OF the trunk of the pneumogastric, which connection takes 

 place close to the exit of the nerve from the skull. It also communicates with 

 ilu pharyngeal plexus as it winds around the occipital artery. (2) It commu- 

 nicates with Tin; SUPERIOR CERVICAL GANGLION of the sympathetic which 

 communication takes place opposite the atlas. (3) It communicates with 



TIIK KIKST AND SECOND CERVICAL NERVES. (4) WlTH THE LINGUAL BRANCH OF 



Tin; fifth which communication takes place near the anterior border of the 

 Hyo-glossus muscle. (Plate CCXXII). 



1 1> branches of distribution are (1) meningeal, which are represented by 

 two filaments given off in the anterior condyloid foramen, pass backward into 

 the posterior fossa of the skull te> be distributed to the dura mater. These 

 nerves are' probably derived from the first and second cervical nerves, the sym- 

 pathetic, or the tenth. It was formerly thought they were' derived from the 

 fifth, (2) Descendens hypoglossi is given off from the twelfth nerve as it 

 passes round the occipital artery. From this point. is passes down over the 

 -heath of the' common carotid artery and joins the' conmmnicans hypoglossi 

 from the second and third cervical nerves just above the middle of the Omo- 

 hyoid muscle. This loop between the descendens hypoglossi anel communicans 

 hpyoglossi is called the' ansa hypoglossi. From this ansa branches are given to 

 the Sterno-hyoid, Sterno-thyroid, and the posterior belly of the Orno-hyoid 

 muscles. A filament from this loop descends into the chest to join the cardiac 

 and phrenic nerves. (3) The thyro-hyoid branch passes from the twelfth 

 nerve near the- posterior border of the Hyo-glossus muscle downward to supply 

 the Thyro-hyoid muscle. (4) Muscular branches are distributed to the 

 following muscle's, (a) Stylo-glossus, (b) Hyo-glossus, (c) Genio-hyoid, (d) 

 Genio-hyo-glossus, (e) to the intrinsic muscles of the tongue. Possibly the In- 

 ferior lingual muscle receives the chorda tympani branch of the seventh. 





Sympathetic System. 

 LESS< >.\ (XIX. ( Plate's ( !XCV-( !X( !VI-( !XCV 1 1-( !XCV I II.) 

 The sympathetic nerve differs from the somatic nerve in four different 

 ways: (1) it has a greal tendency to form plexuses; (2) it has a preponder- 

 ance of Qon-medullated fibres; (3) fibers are' interrupted in nerve cells and (4) 

 its individual nerve fibers are smaller. The sympathetic nerve is the nerve of 

 organic life. If we had nothing but the' sympathetic nerve' it would be in the 

 form of the human body. lis frame work consists of a chain of ganglia extend- 

 ing in fnmt of the- vertebral column, the upper ganglia being on the anterior 



