I.] DISSECTION OF A RABBIT AND OF A DOG. 29 



close to the Glaserian fissure. Break through 

 the bulla, and observe the chorda running 

 across the tympanic cavity over the handle of the 

 malleus (cp. Lesson xxvm.). This course of the 

 chorda tympani may be followed in the rabbit, 

 but the dissection is not easy. 



18. Note also in the tympanic cavity the very small 

 nerve running over the promontory or projec- 

 tion of the cochlea. This is Jacobson's nerve, 

 a branch of the 9th. 



19. Trace up the pneumogastric beyond its ganglion, 

 to its exit from the skull by the foramen jugulare. 

 Note, passing from the skull with the pneumo- 

 gastric, the small spinal accessory nerve 

 behind and the glosso-pharyngeal in front; 

 the communicating branches between these 

 nerves may be neglected. 



20. Trace the glosso-pharyngeal forwards to the 

 tongue and pharynx. It runs nearly in the 

 same direction as, but at a higher level than, the 

 hypoglossal, and may be traced to the hinder 

 part and to the sides of the tongue. 



21. Cut through the above three nerves, a little 

 distance from the skull, break away with small 

 bone forceps the tympanic bulla, and trace more 

 thoroughly the exit from the skull of these 

 nerves and of the hypoglossal. The latter issues 

 through the condyloid foramen, which is separ- 

 ated by a distinct width of bone from the 

 foramen jugulare, through which the other three 

 issue. 



