BROKEN WIND. 
77 
l nucleus of grey matter on the floor of the fourth ventricle, 
tnd by its motor roots from a spot just behind the sensitive 
•oots, and coming from the respiratory tract. It leaves the 
,kull through the foramen lacerum, passes down the neck in 
company with the carotid artery, enters the thorax and from 
here proceeds to the abdomen. Throughout its entire course 
he pneumogastric preserves intimate relations with the great 
sympathetic nerve, numerous anastomosing branches passing 
aetween them. The pneumogastric gives off branches to the 
iharynx, larynx, trachea, bronchial tubes, heart, oesophagus, 
stomach, liver and intestines ; though to what extent its fila¬ 
ments are distributed to the liver and intestines is not 
. 
Known. 
The functions of the pneumogastric nerve that concern us 
it present are : 
1. It gives exquisite sensibility to the mucous membrane 
ining the larynx and bronchial tubes, and is also the sensory 
lerve of the pharnyx, trachea, oesophagus and stomach. 
2. It excites contractions of the muscular fibres of the 
Dronchial tubes. 
3. It provokes movements of the oesophagus and stomach. 
4. It is a stimulating nerve to the respiratory center, 
though its laryngeal branch is inhibitory to that center. 
5. It is the inhibitory nevre of the heart. 
In order that all the organs concerned in respiration may 
let in harmony it is necessary that they be provided with a 
governor. This governor of respiration is called the respira¬ 
tory center, and is situated in the medulla. “ 1 his center may 
oe stimulated directly by the condition of the blood ; an in¬ 
crease of carbon di-oxide or a diminution of oxygen in the 
blood causes an acceleration of respiratory movements, and 
the reverse of these conditions causes a diminution of the 
respiratory movements. 
“ The center may also be stimulated indirectly, by reflex 
action. The medulla may be excited to action through the 
pneumogastric nerves, by the presence of carbon di-oxide in 
the lungs irritating their terminal filaments ; also through the 
fifth nerve by irritation of its terminal branches ; also through 
