988 



THE NERVOUS SYSTEM 



and the internal carotid artery under cover of the parotid gland, the styloid muscles, 

 and the posterior belly of the digastric, and it is crossed superficially by the poste- 

 rior auricular and the occipital arteries. As it turns forwards around the root of the 

 occipital artery the sterno-mastoid branch of that vessel hooks downwards across 

 the nerve, and as it runs forwards on the hyo-glosflUB muscle it lies immediately 

 above the ranine vein. It is crossed by the posterior belly of the digastric and the 

 stylo-hyoid muscle, and it is covered superficially, behind the mylo-hyoid, by the 

 lower part of the submaxillary gland. 



Communications. The hypoglossus is connected with the first cervical gan- 

 glion of the sympathetic, with the ganglion nodosum of the vagus, with the loop 

 between the first and second cervical nerves, and with the lingual nerve; the latter 

 communication is established along the anterior border of the hyo-glossus (figs. 706 

 and 707). 



Terminal Branches. (1) A meningeal branch, frequently represented by two fila- 



FIG. 707. THE HYPOGLOSSAL, GLOSSO-PHAUYNGEAL, AND LINGUAL NERVES. (Spalteholz.) 



GANGLION NODOSUM 



CUT SURFACE OF THE STYLOID 



PROCESS 

 Internal jugular vti/i 



FACIAL NERVE 

 (CUT OFF) 



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 NERVE 



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 BRANCH 



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External carotid artery 1 



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 THIRIt CERVICAL KKIIVK 

 VESrEXltTXi; UK ASCII 



or UYPOGI.OSS \i. 



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 f-'ni-RTH CERVICAL 

 XKR VB 



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 ANSA HYPOGLOSSI 1 



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\ 



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 palatini 



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BRAXCHKX OF 



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 llf HYl'OI.'LOSSAL 

 Hyoelossue Genio-hyoidexia 



Si<p<-i-i"r tliifrfoid artery 

 Thyreo-hyoideus 



\ BKAXCH TO THI-: sri-:itxn-iiY<iiin-:rs 



Common carufi<t <n-ti i-ti 



ments, is given off in the hypoglossal (anterior condyloid) canal. It passes backwards 

 into the posterior fossa of the cranium and is distributed to the dura mater. It 

 w&s believed at one time that the fibres of the meningeal branch were derived from 

 the lingual nerve, but it is now deemed more probable that they are fibres from the 

 cervical nerves, the sympathetic, or the vagus. 



(2) Branches which consist of Fibres derived from the Cervical Plexus. 

 The descendens hypoglossi and the muscular twig to the thyreo-hyoid muscle, though 

 apparent ly arisin? from the twelfth nerve, consist entirely of fibres which have passed 

 into the hypoglossal nerve from the loop between the first two cervical nerves. 



(a) The descendens hypoglossi parts company with the hypoglossus at the 

 point where the latter hooks around the occipital artery (fig. 707) . It runs downwards 

 and slightly inwards on the sheath of the great vessels (occasionally within the 

 sheath), and is joined at a variable level by branches from the second and third 



