148 HAND-BOOK OF PHYSIOLOGY. 



the posterior pulmonary plexuses; and to the Stomach, by its terminal 

 branches passing over the walls of that organ; while branches are also 

 distributed to the Liver and to the Spleen. 



Communications. Throughout its whole course, the vagus contains 

 both sensory and motor fibres; but after it has emerged from the skull, 

 and in some instances even sooner, it enters into so many anastomoses 

 that it is hard to say whether the filaments it contains are, from their 

 origin, its own, or whether they are derived from other nerves combining 

 with it. This is particularly the case with the filaments of the sympathetic 

 nerve, which are abundantly added to nearly all its branches. The likeness 

 to the sympathetic which it thus acquires is further increased by its contain- 

 ing many filaments derived, not from the brain, but from its own petrosal 

 ganglia, in which filaments originate, in the same manner as in the ganglia 

 of the sympathetic, so abundantly that the trunk of the nerve is visibly 

 larger below the ganglia than above them (Bidder and Volkmann). Next 

 to the sympathetic nerve, that which most communicates with the vagus 

 is the accessory nerve, whose internal branch joins its trunk, and is lost 

 in it. 



Functions. The most probable account of the particular functions 

 which the branches of the pneumogastric nerve discharge in the several 

 parts to which they are distributed, may be drawn from John Keid's ex- 

 periments on dogs. They show that, 1. The pliaryngeal branch is the 

 principal motor nerve of the pharynx and soft palate, and is most probably 

 wholly motor; the chief part of its motor fibres being derived from the 

 internal branch of the accessory nerve. 2. The inferior or recurrent 

 laryngeal nerve is the motor nerve of the larynx. 3. The superior laryn- 

 geal nerve is chiefly sensory: .the only muscle supplied by it being the 

 crico-thyroid. 4. The motions of the oesophagus, the stomach and part 

 of the small intestines, are dependent on motor fibres of the vagus, and are 

 probably excited by impressions made upon sensitive fibres of the same. 

 5. The cardiac branches communicate, from the centre in the medullary 

 channel, impulses (inhibitory) regulating the action of the heart. 6. 

 The pulmonary branches form the principal channel by which the sensory 

 impressions on the mucous surface of the trachea, bronchi and lungs that 

 influence respiration are transmitted to the medulla oblongata; and 

 some fibres also supply motor influence to the muscular portions of the 

 fibres of the trachea and bronchi. 7. Branches to the stomach and intes- 

 tines not only convey motor but also vaso-motor impulses to those organs. 

 8. The action of the so-called depressor branch (p. 154, Vol. I.) in inhib- 

 iting the action of the vaso-motor centre has already been treated of, as 

 has also the influence of the vagus in stimulating the secretion of the sali- 

 vary glands, as in the nausea which precedes vomiting (p. 232, Vol. I.). 

 To summarize, therefore, the many functions of this nerve, it may be said 

 that it supplies motor influence to the pharynx and oesophagus, to stomach 



