CARDIAC AND PULMONARY BRANCHES OF THE VAGUS. 6ll 



7. The cardiac branches (fig. 433, g, I), as well as the cardiac plexus, have been 

 described in 57. These nerves contain the inhibitory fibres for the heart (fig. 434, 

 ic cardio-inhibitory Edward Weber, November, 1845 ; Budge, independently 

 in May 1846), also sensory fibres for the heart [in the frog (Budge), and partly 

 in mammals (Goltz)]. Lastly, in some animals the heart receives some of the 

 accelerating fibres through the trunk of the vagus. Feeble stimulation of the vagus 

 occasionally causes acceleration of the beats of the heart (Schiff). [This occurs 

 when the vagus contains accelerator fibres.] In an animal poisoned with nicotin, 

 or atropin, which paralyses the inhibitory fibres of the vagus, stimulation of the 

 vagus is followed by acceleration of the heart-beats (Schiff, Schmiedeberg) [owing to 

 the unopposed action of any accelerated fibres that may be present in the nerve, e.g., 

 of the frog]. 



8. The pulmonary branches of the vagus join the anterior and posterior 

 pulmonary plexuses. The anterior pulmonary plexus gives sensory and motor 

 fibres to the trachea, and runs on the anterior surface of the branches of the bronchi 

 into the lungs (L). The posterior plexus is formed by three to five large branches 

 from the vagus, near the bifurcation of the trachea, together with branches from 

 the lowest cervical ganglion of the sympathetic and fibres from the cardiac 

 plexus. The plexuses of opposite sides exchange fibres, and branches are given off 

 which accompany the bronchi in the lungs. Ganglia occur in the course of the 

 pulmonary branches in the frog (Arnold, W. Stirling) [newt W. Stirling ; and in 

 mammals (Remak, Egorow, W. Stirling)], in the larynx [Cock, W. Stirling], in the 

 trachea and bronchi [W. t Stirling, Kandarazhi\ Branches proceed from the 

 pulmonary plexus to the pericardium and the superior vena cava (Luschka, 

 Zuckerkandl). 



The functions of the pulmonary branches of the vagus are (1) they supply 

 motor branches to the smooth muscles of the whole bronchial system ( 106) ; 

 (2) they supply a small part of the vaso-motor nerves of the pulmonary vessels 

 (Schiff), but by far the largest number of these nerves (? all) is supplied from the 

 connection with the sympathetic (in animals from the first dorsal ganglion) (Brown- 

 Sequard, A. Fick, Badoud, Lichtheim) ; (3) they supply sensory (cough-exciting) 

 fibres to the whole bronchial system, and to the lungs ; (4) they give afferent 

 fibres, which, when stimulated, diminish the activity of the vaso-motor centre, and 

 thus cause a fall of the blood-pressure during forced expiration ; (5) similar fibres 

 which act upon the inhibitory centre of the heart, and so influence it as to accelerate 

 the pulse-beats ( 369, II.). Simultaneous stimulation of 4 and 5 alters the pulse 

 rhythm (Sommerbrodt) ; (6) they also contain afferent fibres from the pulmonary 

 parenchyma to the medulla oblongata, which stimulate the respiratory centre. [These 

 fibres are continually in action], and consequently section of both vagi is followed by 

 diminution of the number of respirations; the respirations become at the same time 

 deeper, while the same volume of air is changed ( Valentin). Stimulation of the central 

 end of the vagus again accelerates the respirations (Traube, J. Rosenthal). Thus, 

 laboured and difficult respiration is explained by the fact that the influences 

 conveyed by these fibres which excite the respiratory centre reflexly are cut off ; so 

 it is evident, that centripetal or afferent impulses proceeding upwards in the vagus 

 are intimately concerned in maintaining normal reflex respiration ; after these 

 nerves are divided, conditions exciting the respiratory movements must originate 

 directly, especially in the medulla oblongata itself ( 368). 



Pneumonia after Section of both Vagi. The inflammation which follows section of both 

 vagi has attracted the attention of many observers since the time of Valsalva, Morgagni (1740), 

 and Legallois (1812). In attempting to explain this phenomenon, we must bear in mind the 

 following considerations : (a) Section of both vagi is followed by loss of motor power in the 

 muscles of the larynx, as well as the sensibility of the larynx, trachea, bronchi, and the lungs, 

 provided the section be made above the origin of the superior laryngeal nerves. Hence, the 

 glottis is not closed during swallowing, nor is it closed reflexly when foreign bodies (saliva, 



