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 tlirough 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-- 



—ou. 



FlO. 196.— Scheme of the Dissection of the Frog's Vagus. SM. Submentalis : LW. Lnng; 

 V. Vagus; GP. Glosso-pharyngeal; Ug. Hypoglossal; L. Laryngeal; PU, SH, GU, 

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

 BR. Brachial plexus. 



(h.) 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 inhihi- 

 tio)}, is manifest in the curve by the lever recording merely a 

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



