The I'etetqna~)'.]omTml 1998, 155, 317-322 +

Gross Anatomy of the Accessory Nerve and Vagus Nerve of the Head and Cranial Neck Region in the Bactrian Camel

CUI-SHENG a n d XIE Z H E N G - MI N G *

Colh'ge of Biolo,ffical Science, China Agricultural University, Beijing, 100094, P.IL China *Department ~( l'etelfnm3.' Medicine, Gansu Agricultural Uniw, rsit~,, Lanzhou, 730070, P.R. China

SUMMARY

Seven heads and necks of Bactrian camels were dissected to investigate the origin, course, b ranches and distr ibution of the accessol T nerve and vagus nerve in the cranial cervical region. T h e spinal roo t and external b ranch of the accesso~ T nerve were not present , but there was a delicate c o m m u n i c a t i n g b ranch between the dorsal root o f the first cervical nerve and the root o f the vagus nerve. T h e s te rnocephal ic muscle was innerva ted by the second cer~dcal nerve while the b rach iocepha l ic and trapezius muscles were suppl ied by the sixth and seventh cervical nerves. In the head and cranial cervical region of the Bactrian camel the vagus nerve gave off the aur icular branch , pharyngea l branch , cranial laryngeal nerve, a c o m m o n t runk to the larynx, oesophagus and trachea, and some c o m m u n i c a t i n g b ranches connec t ing with the g lossopharyngeal , hypoglossal, first cervical ner~'es and the cranial ceradcal ganglion.

KE'CxVORDS: GI'OSS anatomy; Bactrian camel; accessory nerve; vagus nerve; cervical nerve.

INTRODUCTION

T h e Bactrian camel (Camehts bactrianus) is one o f the most i m p o r t a n t domes t ic animals in the deser t and semi-desert areas of China. Al though there are studies of the vagus and accessot T nerves in the d r o m e d a l T camel (Kanan, 1969; Smuts & Bezuidenhout , 1987), there is no in fo rmat ion on the Bactrian camel. Fu r the rmore , the descr ipt ions of the vagus nerve of the dromedary, camel have not been fully detai led and repor t s o f the access- o13, nerve are not in a g r e e m e n t (Kanan, 1969; Wil- lemse, 1958; Smuts & Bezuidenhout , 1987). T h e p resen t study was the re fo re u n d e r t a k e n to give an accoun t o f the accessory nerve and vagus nerve in the head and cranial cervical region o f the Bactr- ian camel .

Correspondence tt~: Dr Cui-Sheng, College of Biological Science. China Agricuhural University. Be!jing, 100094, P.R. ( :hina.

MATERIALS AND METHODS

T h e heads and necks of seven a d u h Bactrian camels were col lected in I n n e r Mongol ia of China and fixed by infusion of 10% formal in t h rough the c o m m o n carot id artery as descr ibed previously (Cui Sheng, 1996b). Both sides of each spec imen were dissected to observe the gross ana tomy o f the vagus nera,e, accessory nerve and the innervat ion of the s ternocephal ic , b rach iocepha l ic and trapez- ius muscles.

RESULTS

Accessory nerve (N. a c c e s s o r i u s ) N o n e of the dissections revealed the p resence

of the spinal roo t o f the accessory nerve. However , one single delicate bund le was found to arise f rom the dorsal root to the first cervical nerve, course cranially in the atlantal canal and then pass

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318 THE VETERINARY JOURNAL. 155. 3

I I I M e d u l l a r y o b l o n l a t s Spinal cord I

i i Cl el IT X X IX

Fig. 1. R e p r e s e n t a t i o n o f a naould o f the cervical ne rves a n d wtgtts ne rve in the Bactr ian camel . C I. First cevvical nerve . ( '2. S e c o n d cervical nerwe. XlI . Hypoglossa l nerve . X. Vagus nerve . IX. Glossopha l3 'ngea l nen , e . 1. Ven t ra l r o o t , , f t he s e c o n d cervical nerve . 2. Dorsal r o o t o f t he s e c o n d cervical nerve . 3. Ven t ra l roo t o f t he first cervical nerve . 4. Dorsal r o o t o f t he first cervical nerve . 5. T h e c o m m u n i c a t i , l g b, 'ancla b e t w e e n the do, 'sal r o o t o f the first ce ,vical ne,-ve a n d the roo t o f vagus nerve . 6. Dorsal , 'oot o f hypoglossa l ne rve ( D e s c r i b e d previously by Cui S h e n g , 1996b). 7. Cra, l ial g a n g l i o n o f v;.I.gus nerve.

through tile foramen magnum to jo in the root of the vagtts nerve intracranially (Fig. 1) The medul- la D, roots of the accessol T nerve could not be sep- arated fi'om the vagal root and there was no dis- tinct accessory nerve in the neck.

Vagus nerve (N. vagus) The vagus nerve (Fig. 1) emerged fi'om the lat-

eral aspect of the medulla oblongata by a series of rootlets, coursed lateroventrally, and then united to form a t runk near the jugular tbramen where it forlned its cranial ganglion. After leaving the cran- ial cavit T, the vagus nerve (Fig. 2) coursed caudo- ventrally, medial to the tympanic bulla and on the rostrolateral aspect of the longus capitis muscle. It then uni ted ventral to the atlantoaxial jo in t with the sympathetic t runk to constitute the vagosym- pathetic trunk. In the head and cranial cervical region, the vagus nerve gave off the attricular branch, pharyngeal branch, cranial laiTngeal nera,e, tile c ommon trtink to the larynx, oesoph- agus and u-achea, some branches connect ing with the glossophaD, ngeal nerve, hypoglossal nerve, first cervical nerve and the cranial cervical ganglion.

The audcular branch (Ramtts auricularis). The atu'icular branch (Ramus attricularis) arose from the cranial ganglion, turned upwards in the jugu- lar foramen and then travelled dorsally in the fis- sure between the petrosus part and the juguhu" process of the tenaporal bone. After receiving a comnaunicating branch ti-om tile glossopharyn- geal nerve in the fissure, the aurictdar branch con- t inued to ascend in a small canal of tile temporal bone and then en tered tile facial canal near the swlomastoid tbralnen, in which it jo ined the tacial n e i 've.

The phao, ngeal branch. The phaiTngeal branch (Ram.us phmyngeus) originated from the vagus nerve ventral to the wings of tile atlas (Fig. 2) and passed ventrally over the rostral part of tile cranial cervical ganglion and internal carotid artery to gain the dorsal wall of the phal-ynx. Here the branch divided into cranial and caudal branches. The cranial branch coursed ,'ostroventrally and then .joined the phalTngeal branch of the glosso- phal3,ngeal nerve. The caudal branch coursed caudoventrally oil the dorsolateral surface of the pharynx and sent Ibm" or five branches to supply tile thyropharyngeus, cricol)haryngeus, hypo-

ACCESSORY AND VAGUS NERVES OF THE BACTRIAN CAMEL 319

1 2 3

15

16

17

18

19

24 23 22 zl ZU

Fig. "7. The vagus nerve in the head and cranial neck region of the Bactrian camel. 1. Glossopharyngeal nerve. 2. The communicating branch beo,~,een glossopharvngeal nerve and vagus nerve. 3. Vagus nen,e. 4. Hypoglossal nerve. 5. Ventral branch of the first cervical nerve. 6. M. obliquus capitis (cranialis). 7. PhmTngeal branch of vagus nerve. 8. M. rectus capitis ventralis. 9. M. longus capitis. 10. Cranial laryngeal nerve. 11. The common trunk to the larynx, oesophagus and trachea of vagus nerve. 12. Cervical sympathetic trunk. 13. Vagosympathetic trunk. 14. Oesophagus. 15. M. Iongissimus capatis. 16. M. obliquus capitis caudalis. 17. M. Iongissimus atlantis. 18. Communicating branch between cranial laryngeal nerve and caudal lat3~ageal nerve. 19. Oesopbageal and tracheal branch of common trtmk to dae larynx, oesophagus and trachea of vagus nerve. 20. Caudal laryngeal nerve. 21. M. cricopharyngeus. 22. M. cricothyroideus. 23. M. tbyropharyngeus. 24. Communicating branch between pharyngeal branch and cranial lal3qageal nerve of vagus nerve. 25. M. thyrohyoideus. 26. M. stylohoideus. 27. Internal branch of cranial laryngeal nerve. 28. Caudal branch-of pharyngeal branch of vagus nerve. 29. Lingual brancb of glossopharyngeal nerve. 30. Cranial branch of pharyngeal branch of vagus nerve. 31. Pharyngeal branch of glossopharyngeal nerve. 32. M. stylopharyngeus caudalis. 33. Mandibular nerve.

pharyngeus muscles and the lateral wall of the pharynx. One of those branches connec ted with the external branch of the cranial laryngeal nerve on the dorsolateral aspect of the thyropharyngeus muscle.

The cranial laryngeal nerve. The cranial lar- yngeal nerve (Ramus la~yngeus cranialis) arose in four specimens from the vagus nerve caudal to the pharyngeal branch. In others it arose from the original part o f the c o m m o n trunk to the larynx, oesophagus and trachea. The cranial laryngeal nelwe coursed caudally on the thyropharyngeus muscle for a short distance and then divided into internal and external branches.

The external branch. The external branch (Ramus externus) coursed caudoventrally on the dorsalolateral surface of the thyropbaryngeus muscle and gave off branches to supply the thyro- pharyngeus, cricopharyngeus, cricothyroideus, and hyopharyngeus muscles and thyroid gland. The cont inuat ion of the branch jo ined the caudal laryngeal nerve at the caudal border of; the crico- pharyngeus muscle. The external branch also received a communica t ing branch of the glosso- pharyngeal nerve on the external wall of the pharynx.

The internal branch. The internal branch (Ramus internus) coursed ventrally on the lateral

320 THE VETERINARY ,IOLIRNAL, 155, 3

surface of the thyrophaD.,ngeus muscle and then pene t r a t ed the thyroid fo r am en to gain the dorsal- olateral aspect o f the thyroaD, t eno ideus mnscle where the internal b ranch ramif ied and suppl ied the lalTngeal mucosa. O n e of these b ranches coursed caudally on the dorsolateral surtace of the thyroepiglot t ic inuscle and c o n n e c t e d with the b ranch of the caudal laiTngeal nerve at the ventral b o r d e r of the dorsal c r icoalTtenoideus lnuscle.

The common trunk to the launx, oesophagus and trachea

T h e c o n n n o n t runk to the laITnx, oesophagus and t rachea or ig ina ted f rom the vagus nerve jus t caudal to the cranial laryngeal nerve, coursed cau- doventrally, medial to the c o m m o n carot id ar tery and on the dorsalolateral aspect o f the thyro- pha ryngeus and cricophaD, ngeus mnscles. After ga in ing the caudal b o r d e r of the c r i copharyngeus muscle, the t runk gave off the caudal laryngeal nerve. T h e cont inua t ion o f the t runk coursed be tween the t rachea and oesophagus and sent off some b ranches to supply the t rachea and oesophagus .

The caudal laungeal nen,e T h e caudal larTngeal neree (N. &Wlgeus

caudalis) received a c o m m n n i c a t i n g hrancla of cranial lalTngeal nerve at its origin and then tu rned rostrally, coursed u n d e r the c r icopharyn- geus muscle and sent off b r anches to supply the cricoaD, t eno ideus lateralis, cricoaD, tenoideus dor- salis and a lTtenoideus transversus muscles. O n e of these b ranches c o n n e c t e d with the in ternal b ranch of the cranial l awngea l nerve at the ven- tral b o r d e r of the cr icoaiTtenoideus lateralis muscle.

Comm.unication branches T h e vagus nerve c o n n e c t e d with o the r nerves by

the following c o m m u n i c a t i n g branches: one b ranch arose f rom the vagus nerve on the rostrola- teral aspect o f the rectus capitis ventralis nmscle and coursed rostrally and dorsally, connec t i ng with the glossophai.wngeal nerve media l to the tympanic bulla; two b ranches or ig ina ted f rom the vagus nerve on the lateral aspect o f the rectus cap- itis ventralis muscle, coursed dorsocaudal ly and c o n n e c t e d with the hypoglossal nelwe; one b ranch arose fi 'om the vagus nerve nea r the caudovent ra l b o r d e r o f the rectus capitis lateralis muscle, con- nec t ed with the ventral b r anch of the first cervical nmwe ventral to the wing o f the atlas. In addi t ion,

neal- the caudodorsa l b o r d e r of the cranial cervi- cal gangl ion, the vagus nerve sent off three short c o m m u n i c a t i n g h ranches to connec t with the cranial cervical gangl ion.

The nerve supply of the stenlocephalic, brach.iocephalic and trapezius muscles

T h e s te rnocepha l ic muscle was innerva ted by the ventral b r anch of the second cervical nerve. T h e ventral b ranch arose fi 'om the second cel-vical nerve outside the in terver tebra l tbra lnen and then coursed ventrolateral ly between the obl iquus cap- itis caudalis inuscle and inter- transversarius lnus- cle. After ga in ing the medial aspect o f the j ugu l a r vein, the ventral b ranch gave off one small b ranch , which coursed caudoventra l ly medial to the j ugu l a r vein, and then ramif ied to supply the s te rnocepha l ic muscle.

T h e trapezius and b rach iocepha l i c muscles were innerva ted by the ventral branclaes of the sixth and seventh cervical nerves. T h e ventral b ranch of the sixth cervical nerve gave off one b ranch lateral to the in terver tebra l f iwamen coursed caudally medial to the b rach iocepha l i cus lnuscle and then ramif ied to supply the hrachioce- phalic and trapezius muscles. T h e ventral b ranch of the seventh cervical nerve gave off one brancla lateral to the in terver tebra l f o r amen , which coursed upward and backward and then tu rned over the transverse process of the seventh cervical ve r tebra and ga ined the medial aspect o f the ster- nocepha l i c muscle. He re it ramif ied and suppl ied the t rapezius muscle.

DISCUSSION AND CONCLUSIONS

T h e presen t study d e m o n s t r a t e d that there is a delicate nerve bundle , which or iginates f rom the dorsal root o f the first cervical nerve and connec t s to the roo t o f the vagus nerve. This appea r s to be a c o m m u n i c a t i n g b ranch be tween the tirst celM- cal nerve and vagus nerve. In the d r o m e d a r y camel , a similar nela.'e f ibre arises fi 'om the dorsal roots o f the first cervical nerve (Kanan, 1969) or be tween the dorsal root and ventral roo t o f the first cervical nerve (Smuts & Bezu idenhou t , 1987), and is descr ibed as the spinal root o f the accessoi T nerve. F u r t h e r m o r e , the dorsal root o f the first cervical nerve in the Bactr ian camel is a lmost as large as that of the second ceiwical nerve (Cui, 1995a), a l though the dorsal root o f the first cervi- cal nerve is usually smal ler than that o f the second

ACCESSORY AND VA(_;US NERVES OF THE BACTRIAN CAMEL 321

cervical nerve in o the r domes t ic animals (Goh indo & Getty, 1975a, b). I n d e e d in some h u m a n specimens , the dorsal root o f the first cer- vical nerve is absent and a root f rom the accesso~ T nerve joins the ventral root o f the f r s t cervical nerve (Pearson, 1969). Thus the origin of the c o m m u n i c a t i n g b ranch between the first cervical nerve and vagus nerve and the relat ions of this c o m m u n i c a t i n g b ranch to the first cmMcal nerve need to he identif ied by the furtlaer microscopic ana t omy or histological research in the Bactrian camel.

T h e caudal par t of" the vagal rootlets o f the Bactrian camel is similar to the medul lm T root of the accessory nerve of o the r animals (GetD', 1974a, h; Xie, 1987). However , these rootlets do not tb rm a separa te t runk in the Bactrian camel and in te rmingle with the vagus nerve. This a r r a n g e m e n t bears a close morpho log ica l resem- blance to that in h u m a n ana t om y (Pearson, 1969) but is unlike the usual a r r a n g e m e n t in o the r animals.

In the Bactrian camel the trapezius and brachi- ocephal ic muscles are innerva ted by the sixth and seventh cervical nerves, while in the dromedaD*, the innervat ion is only by the seventh cervical nerve ( I~man, 1969). Furthermore , the s ternoce- phalic muscle is innerva ted only by the second cervical nerve in the Bactrian camel (Cui Sheng, 1995a; Willense, 1958) but by both the first and second nerves in the d r o m e d a r y (Kanan, 1969).

T h e vagus nerve o f the Bactrian camel is similar to that o f o the r animals and the c o m m o n t runk to the laD, nx, oe sophagus and t rachea in Bactrian camel does not differ fl-om that o f the d l 'omedal T (Smuts & Bezuiden lmut , 1987).

Al though in the dog and pig (Godinho , 1973; GetD', 1974b), the vagus nerve has bo th a cranial and a caudal gangl ion, in the Bactrian camel as in the horse, ox and sheep (God inho & Getty, 1974a; Xie, 1987), the caudal gangl ion is not visible.

T h e results r epo r t ed in this p a p e r indicate that there are unusual features of the cervical, vagus and accessory nerves in the Bactrian camel . Fur the r studies using m o r e specific stains for ner-

vous tissues in the brain and spinal cord o f bo th the Bactrian and d r o m e d a r y camels should br ing interest ing facts to light, part icularly conce rn ing the spinal nucleus o f the accessory nerve.

ACKNOWLEDGEMENTS

T h e authors wish to thank Professor A. S. McNe- ill),, MRC Reproduct ive Biology Unit, Ed inburgh , Scotland, for reviewing the English manuscr ip t .

REFERENCES

Ct'l, Slll~X¢; (1996a). Tile first and second cervical nerves of tile Bactrian camel. Journal of Lanzhou Uni- versity (Natural Sdence) 31 (Morphology, Suppl.), 117-20 (in Chinese).

CH, Sm.:s¢. (1996b). Gross anatomy of the hypoglossal nerve in the Bactrian camel. Journal of Lanzhou Uni- versitr (Natural Science) 31 (Morphology, Suppl.), 123-5 (in Chinese).

GODINIIO, H. P. (1973). Nerve of the restrophmTngeal ,egion in swine. Arquivos da Escola de Vete~naria da Univer~idade Federal de Minas Gerais 25, 49-53.

G~Dlxlto, H. P. & GI-TvI-';, R. (1975a). In Sisson and Gross- man The Anatomy of the Domestic Animals, Volume 1, Fifth edition, ed. R. Getty, pp. 660-3, 1092-126. Phil- adelphia, London, Toronto: W. B. Saunders Company.

Got~lxHo, H. P. & (h.:vm, R. (1975b). In Sisson and Gross- man The ,-lnalomv of the Domeslic Animals, Volume 2, Fifth edition, ed. R. Getty, pp. 1381-3, 1692-5. Phila- delphia, London, Toronto: W. B. Saunders Company.

K~x.~x, C. V, (1969), Spinal accessory nerve of the camel. Acta ,4 natomica 74, 615-23.

PL~RSOX, A. A. (1969). Tim accessory nerve and its relation to the upper spinal nerve. A~ne~ican./ournal of Anatomy 114, 371-91.

StaTs, M. M. S. & BEZt'mEXiU~t'r, A.J. (1987). Anatomy of the dmmedm)'. Oxford: Clarendon.

WnJJ-:xls~:, J. J. (1958, Cited by Pearson, A. A. (1969)). The accessory nerve and its relation to the upper spi- nal nerve. A~tericanJournal ofAnalomy 114, 371-91.

Xu-, Z. M. (1987). On-The-Spot Anatomy of Donkm' and Horse, Second Edition, 114, 371-91. l~,e!jing: Agricul- ture Press (in Chinese).

(Accepted fi, r publication 26.lure, 1997)