NINTH PAIR OF NERVES. 



721 



NINTH PAIR OF NERVES (Nervi 

 hypoglossi, vel gustatorii, Winslow; Linguttlis, 

 Vic d'Azyr : Ninth nerve of Willis ; Twelfth of 

 Scemmering.) The ninth pair of nerves take 

 their origin from the side of the medulla ob- 

 longata, commencing by a variable number of 

 small radicles in the fissure which separates 

 the corpus olivare from the pyramidale. 



The superior of these radicles are attached 

 about the centre of this fissure, and the infe- 

 rior a little below its termination; they are 

 placed on a line one below the other, which 

 line describes a slight curve looking upwards 

 and backwards, following the curved form of 

 the olivary body. 



The origin of this nerve is superior to that 

 of the first cervical, to which also it lies on a 

 plane a little anterior ; it is separated from the 

 origins of the par vagum by the olivary body, 

 and has lying immediately in front the corpus 

 pyramidale and the vertebral artery. 



The radicles which form the origin of this 

 nerve vary in number from five to ten or 

 twelve ; and if any of these radicles be ex- 

 amined closely, they will be found to consist of 

 two or more minor filaments, so that it is very 

 difficult to say exactly by how many roots or 

 origins the ninth nerve is attached to the me- 

 dulla spinalis.* 



These filaments in general unite into two 

 fasciculi, which pass in a direction downwards,, 

 forwards, and outwards to the anterior condy- 

 loid foramen, through which the nerve escapes 

 from the cavity of the cranium. 



It rarely happens that these fasciculi unite 

 in the cavity of the cranium ; in general, they 

 pass on separately until they reach the foramen, 

 where in passing through the dura mater they 

 become united into one trunk, which is here 

 invested with a strong neurilemma, derived 

 from the dura mater. 



The ninth pair of nerves, on emerging from 

 the anterior condyloid foramen, is in close re- 

 lation to the eighth pair of nerves, the internal 

 carotid artery, internal jugular vein, and with 

 the superior cervical ganglion of the sympa- 

 thetic. 



Here the nerve lies external to the vagus. 

 Connected to it by a dense cellular tissue, for a 

 space about the eighth of an inch, it passes 

 behind the internal carotid artery immediately 

 before that vessel enters the carotid canal, and 

 lies in front of the jugular vein ; here also the 

 nerve is connected to the anterior and superior 

 patt of the superior cervical ganglion, in a 

 manner to be presently described. 



In this situation the ninth nerve lies deep in 

 the neck, being covered by the origins of the 

 styloid muscles, the posterior belly of the di- 

 gastric, the sterno-mastoid, the skin, platysma, 

 and fascia. 



The trunk of the nerve then passes down- 

 wards, outwards, and slightly forwards, escapes 

 from beneath the posterior belly of the digas- 



* Quarum incertus numenis causa est, cura a 

 variis varie descripts et delineatae cxstent. Alii 

 enim quat^or, alii octo compoiii fasciculis dixe- 

 runt. Scemmering de Basi encephali et originibus 

 ncrvoiuui, jicige 168. 



VOL. III. 



trie and anterior edge of the sterno-mastoid, 

 becomes more superficial, is crossed in this 

 part of its course by the occipital artery, and 

 at a point in the neck corresponding to the 

 level of the third cervical vertebra,* and 

 opposite the angle of the jaw,f the nerve 

 turns forwards and upwards, forming an 

 arch, the convexity of which looks downwards 

 and backwards; here the nerve is covered only 

 by the skin, platysma, and fascia, crosses and 

 lies in front of the origin of the occipital 

 artery, the internal jugular vein, external ca- 

 rotid artery, and vagus nerve ; passing still in- 

 wards and upwards towards the posterior edge 

 of the hyoglossus muscle, the nerve is crossed 

 by the tendon of the digastric, lying here su- 

 perior to the lingual artery. 



Itthen passes between themylo-hyoid and the 

 hyo-glossus,and having reached the anterior edge 

 of the last-named muscle, it enters and passes 

 through the fibres of the genio-hyoglossus, in 

 the substance of which muscle it divides into 

 its terminating branches, the connections and 

 distribution of which shall be examined after 

 we have considered the connections of this 

 nerve and the branches which it gives off and 

 receives in its course through the neck. 



The ninth nerve, on escaping from the an- 

 terior condyloid foramen, is connected to the 

 par vagum, as was before noticed, by dense cel- 

 lular tissue, but also by a nervous filament; 

 further on, as the ninth nerve approaches the 

 transverse process of the atlas, it receives a 

 twig from the first cervical nerve, or from the 

 nervous loop formed round the transverse 

 process of the atlas by the communicating 

 branches of the first and second cervical 

 nerves. J 



In this situation, also, the ninth is connected 

 by a small nerve with the superior cervical gan- 

 glion. 



Rumus cervicalis descendens, sen descendens 

 noni. The next regular branch given off by 

 this nerve is immediately before it turns in front 

 of the jugular vein and carotid artery, when it 

 gives off a large and regular branch called cer- 

 vicalis descendens, or descendens noni. 



The point at which the ninth nerve gives off 

 this branch is immediately below the angle of 

 the jaw, and where it escapes from under the 

 edge of the sterno-mastoid muscle. The de- 

 scendens noni from this passes downwards and 

 forwards to the inferior part of the neck ; at 

 its origin this nerve frequently receives a twig 

 from the par vagum ; it passes down the neck 

 in front of the jugular vein and carotid artery, 

 crossing these vessels obliquely, being in this 

 course superficial to the cellular investment de- 

 rived from the cervical fascia which constitutes 

 the sheath of these vessels. 



Omo-hyoid brunch. About the centre of the 

 neck, the cervicalis descendens gives off a con- 

 siderable branch, which, passing in a direction 

 upwards and inwards, enters the interior belly 



* Soe Meckel, Manuel d'Anatomie, vol. iiL 

 page 53. 



t See Boyer, Traitc d'Anatomie, vol. iii. p. 359. 

 \ See Traitc d'Anatoniie, iioycr, vol. iii. p. 359. 



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