274 



PRACTICAL PHYSIOLOGY. 



[LVL 



the tongue, above it is the vagus in close relation 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 

 exposed outside the cranium., is the vago-sympathetic. The 

 glosso-pharyngeal and vagus leave the cranium through the same 

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

 the sympathetic enters the skull. 



2. Stimulation of the Cardiac Vagus. 



(a.) Adjust a Gaskell's heart-lever to record the contractions of 

 the heart on a revolving drum moving at a slow rate. 



SM 



GP--- 



--HB 



1-PK 



X--OK 



'LIT 



FIG. 196. Scheme of the Dissection of tlie Frog's Vagus. SM. Submentalis ; LIT. Lung; 

 V. Vagus; GP. Glosso-pharyngeal; tig. Hypoglossal; L. Laryngeal; PH, SH, GH, 

 OH. Petro-, Sterno-, Genio-, Omo-hyoid ; HB. Hyoid ; HG. Hyoglossus ; H. Heart; 

 ER. Brachial plexus. 



(b.) Place well-insulated electrodes under the trunk of the vagus. 

 Take a normal tracing, and then stimulate the vagus with an inter- 

 rupted current, and observe that the whole of the heart is arrested 

 in diastole. The best form of electrodes is the fine shielded elec- 

 trodes shown in fig. 227. Although the faradisation is continued, 

 the heart recommences beating. The arrest, or period of inhibi- 

 tion, is manifest in the curve by the lever recording merely a 

 straight line. If the laryngeal muscles contract, and thereby affect 



