2I 4 



HEAD AND NECK 



view. Pass the knife downwards, anterior to the medulla 

 oblongata, into the vertebral canal, and, cutting firmly back- 

 wards and laterally, on each side, divide the medulla spinalis 

 and the vertebral arteries. Withdraw the knife, pass two 

 fingers downwards anterior to the medulla oblongata and lift 

 it and the pons and the cerebellum out of the posterior fossa. 

 Place these lower parts of the brain, which collectively 

 constitute the hind brain, with the hemispheres previously 



Oculo-motor nerve 



Trochlear nerve 



Sensory root of the trigemmal nerve 

 Motor root of the trigeminal 

 nerve 



Abducent nerve 



r root of facial 

 Cut edge of the 

 tentorium 



Mote 



Sensory root of 

 facial nerve 

 Acustic nerve 

 Right transverse 

 sinus 



osso-pharyngeal 

 nerve 

 Vagus nerve 



Accessory nerve 



Vertebral artery 

 Hypoglossal nerve 

 First spinal nerve 

 Accessory nerve 



FIG. 90. 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. 



removed, and then examine the cut ends of the cerebral nerves 

 and the blood sinuses which lie in the region of the posterior 

 fossa. 



In the upper end of the vertebral canal lies the 

 upper extremity of the severed medulla spinalis, attached 

 on either side to the margin of the foramen magnum by 

 the uppermost dentation of the ligamentum denticulatum. 

 Anterior to the ligamentum denticulatum, on each side, is 

 the vertebral artery, and still more anteriorly, on a slightly 

 deeper plane, the fila of the anterior root of the first cervical 



