EXPERIMENTAL PHYSIOLOGY. 



the sternum, and pull the fore-legs well apart. Introduce a 

 small test-tube, or stick of sealing-wax into the oesophagus, 

 to distend it; the nerves leaving the cranium are better 

 seen winding round from behind when the oesophagus is dis- 

 tended. Remove the muscles covering the petrohyoid 

 muscles which reach from the petrous bone to the posterior 

 horn of the hyoid bone (Fig. 98). Three nerves are seen 

 coursing round the pharynx parallel to these muscles. The 

 lowest is the hypoglossal (H), easily recognised by tracing it 

 forward to the tongue, above it is the vagus in close relation 



sai 



GP--- 



Fig. 98. Scheme of 

 LU, lung; 

 Laryngeal 

 HB, hyoid ; HG, hyoglossus ; H, heart ; BR, brachial plexus. 



with a blood-vessel (V), and still further forward is the glosso- 

 pharyngeal (GP). Observe the laryngeal branch of the 

 vagus (L). The vagus, as here exposed outside the cranium, 

 is really the vago-sympathetic. The glossopharyngeal and 

 vagus leave the cranium through the same foramen in the 

 ex-occipital bone, and through the same foramen the sympa- 

 thetic enters the skull. 



