2l8 



HEAD AND NECK 



and the internal carotid artery, but soon they choose 

 different routes. The accessory inclines backwards, superficial 

 or deep to the internal jugular vein ; the glosso-pharyngeal 

 runs forwards, superficial to the internal carotid, and under 

 cover of the posterior belly of the digastric ; at a lower 

 level, the hypoglossal also turns forwards across the internal 

 and external carotid arteries; and the vagus proceeds 



Oculo-motor nerve 



Trochlear nerve 



Sensory root of the trigeminnl nerve 

 Motor root of the trigeminal 

 erve 



Abducent nerve 



otor root of facial 

 nerve 



Cut edge of the 

 tentoriuin 



- Sensory root of 



facial nerve 

 Acoustic nerve 

 Right transverse 

 sinus 



Glosso-pharyngeal 

 nerve 

 Vagus nerve 



Accessory nerve 



Vertebral artery 

 Hypoglossal nerve 

 First spinal nerve 

 \ccessory nerve 



FIG. 8 1. Section through the Head a little to the right of the Median Plane. 

 It shows the posterior cranial fossa and the upper part of the vertebral 

 canal after the removal of the brain and the medulla spinalis. 



vertically downwards, first between the internal jugular vein 

 and the internal carotid artery, and then between the vein 

 and the common carotid artery (Fig. 79). 



In an ordinary dissection it is impossible to follow out many of the 

 minute twigs which take origin from the last four cerebral nerves in the 

 region of the basis cranii. To do so it is necessary to possess a perfectly 

 fresh part which has been specially prepared by having the soft parts 

 toughened with spirit and the bone softened by immersion in a weak 

 solution of acid. Even then the dissection is a difficult one, but it should 

 be undertaken by the advanced student, in the event of his being able to 

 obtain a part for the purpose. 



