722 



NINTH PAIR OF NERVES. 



of the omo-hyoid muscle, in the substance of 

 which it ramifies. 



Plexus. Immediately below the tendon of 

 the omo-hyoid, the descendens noni, uniting 

 with branches given off by the second and 

 third cervical nerves, forms a nervous arch, the 

 convexity of which looks downwards and for- 

 wards. This plexus lies under cover of the 

 sterno-mastoid, and in front of the jugular 

 vein. 



Sterno-hyoid and thyroid branches. From 

 the convexity of the arch formed by this plexus 

 two or sometimes more nerves proceed down- 

 wards and inwards, and ramifying on the super- 

 ficial surface of the sterno-hyoid and thyroid 

 muscles, are distributed to them. 



Cardiac branch. Meek el states, that on the 

 left side particularly he has been able to trace 

 a branch from this plexus into the thorax along 

 the pericardium as far as the heart. The cervi- 

 calis descendens is observed sometimes to vary 

 from the above description, in its course down 

 the neck, and in its relation to the great vessels; 

 for, instead of lying anterior and external to 

 the sheath, it is occasionally found to pass down 

 within the sheath, and sometimes even behind 

 it. I have also seen it pass for a short dis- 

 tance within the sheath in the upper part of its 

 course, becoming superficial about the centre 

 of the neck, and then running down in front 

 of the sheath in the usual manner. 



These varieties in the course and relations of 

 this nerve are not, however, very commonly 

 met with. 



Thyro-hyoid branch. The next branch given 

 off by the ninth pair is where the nerve is 

 passing under the tendon of the digastric, a 

 little above the cornu of the os hyoides. Here 

 it gives off a considerable branch named thyro- 

 hyoid, from its distribution. This nerve passes 

 from its origin downwards and inwards, cross- 

 ing the lingual artery, to which it lies super- 

 ficial, and is distributed to the thyro-hyoid 

 muscle. 



From the origin of the thyro-hyoid branch 

 the ninth nerve passes inwards between the 

 hyoglossus and mylo-hyoid muscles, and at the 

 anterior edge of the hyoglossus it plunges into 

 the genio-hyoglossus, in the substance of which 

 its terminating branches ramify. In this course 

 the ninth nerve supplies filaments to the mylo- 

 hyoid, the hyoglossus, the genio-hyoid, genio- 

 hyoglossus, and lingualis. 



In the substance of the genio-hyoglossus the 

 branches of the ninth nerve form distinct anas- 

 tomoses with branches of the fifth (the gusta- 

 tory) ; with this nerve the branches of the 

 ninth form nervous loops or arches, the con- 

 vexities of which look forwards, and from which 

 branches pass off which may be traced to the 

 mucous membrane of the tongue. There can 

 be little doubt that these nerves are to be con- 

 sidered as compound, containing filaments de- 

 rived both from the ninth and fifth pair. Most 

 anatomists state, that the ultimate branches of 

 the ninth can be traced no further than the 

 structure of the muscles which enter into the 

 formation of the tongue, and this appears to be 

 true with respect to the branches which do not 



anastomose with the fifth pair ; but it is more 

 than probable, although difficult to demon- 

 strate, that from the anastomosis spoken of 

 above, a nerve, composed of filaments both 

 of the ninth and fifth, proceeds, and is 

 distributed to the mucous membrane of the 

 tongue. 



Comparative anatomy. It has been asserted 

 by Professor Mayer, that in the ox and some 

 other Mammalia he has discovered a small 

 posterior root to the ninth nerve, having on it 

 a ganglion ; to the investigation of this I have 

 paid particular attention. I have repeatedly 

 and with care sought for this posterior root and 

 ganglion in the ox, and have never been able 

 to satisfy myself as to the existence of a true 

 posterior root to this nerve. 



The anatomy, however, of this part in the ox 

 is extremely interesting, and when examined 

 may, perhaps, explain Mayer's opinion. 



In the dissections which I have made of the 

 ninth pair in the ox, the nerve was found to 

 arise in the depression between the corpus 

 olivare and pyramidale by several delicate 

 roots, in a manner very similar to what is ob- 

 served in the human subject ; these roots uni- 

 formly formed two bundles, which perforated 

 the dura mater separately, before doing which, 

 however, the most inferior of these two bundles 

 received a twig, which at first sight appeared 

 to be given off by the spinal accessory ; but, 

 upon further and careful dissection, this twig 

 was found not to come from the spinal acces- 

 sory, but to arise by a number of distinct roots 

 from the side of the medulla spinalis, anterior 

 to the roots of the spinal accessory, in front of 

 and distinct from which it passed up into the 

 cranium, and joined the inferior of the two 

 bundles, which formed the origins of the ninth, 

 and uniting with this passed out through the 

 anterior condyloid foramen. 



When this nerve was cleansed, the pia mater 

 and coagulated blood removed, which always 

 loads these parts in the slaughtered ox, no en- 

 largement or any thing resembling a ganglion 

 could be discovered on its course. This nerve 

 cannot be considered a posterior root to the 

 ninth pair, for its origin from the medulla is 

 anterior to that of the spinal accessory ; and I 

 am inclined to think that this nerve in the ox 

 holds the same relation to the ninth that the 

 spinal accessory does to the eighth. Can this 

 be what Mayer supposes to be a posterior root 

 to the ninth ? 



VVinslow speaks of a communication be- 

 tween the spinal accessory and ninth nerve 

 within the cranium, the existence of which in 

 the human subject is described by Scarpa and 

 Meckel ;* I have never been able to trace any 

 such communication in man. 



On tracing the ninth nerve in the ox through 

 the anterior condyloid canal, it was found to be 

 united into one trunk, and enveloped with a 

 strong neurilemma; nor could any ganglion 

 be detected on the nerve in this part of its 

 course. 



In Birds, the ninth nerve is found to cominu- 



* See Manuel d'Anatomic, Meckel, vol. iii. p. 59. 



