VIBRATIONS COMMUNICATED TO THE BODY BY THE HEART. 157 



against the upper teeth, owing to the pulse-beat in the external maxillary artery 

 raising the lower jaw. The second elevation is clue to the closure of the semi- lunar 

 valves, and not to a dicrotic wave. 



6. Brain and Fontanelles. The large arteries at the base of the brain com- 

 municate a movement to it, while similar movements occur with respiration rising 

 during expiration and falling during inspiration. These movements are visible 

 in the fontanelles of infants. The respiratory movements depend upon variations in 

 the amount of blood in the veins of the cranial cavity, and also upon the respiratory 

 variations of the blood -pressure. 



7. Amongst pathological phenomena, are the beating in the epigastrium, as in 

 hypertrophy of the right or left ventricle, caused, it may be, by deep insertion of 

 the diaphragm, and it may be partly by the beating of a dilated abdominal aorta or 

 coeliac axis. 



Abnormal dilatations (aneurisms) of the arteries cause an abnormal pulsation, 

 while theyproducea slowing inthe velocity of the pulse-wave in the corresponding artery. 

 Hence the pulse appears later in such an artery than in the artery on the healthy 

 side. Hypertrophy and dilatation of the left ventricle cause the arteries near the 

 heart to pulsate strongly. In the analogous condition of the right ventricle, the beat 

 of the pulmonary artery may be seen and felt in the second left intercostal space. 



80. Vibrations communicated to the Body by the 



action of the Heart, 



The beating of the heart and large arteries communicates vibrations to the body 

 as a whole, but the vibration is not simple but compound. 



Gordon was the first to represent this pulsatory vibration graphically. If a 



B 



/LL 



n 



Fig. 70. 



II, Elastic support for registering the molar motions of the body K, a wooden 

 box ; B, feet of patient ; p, cardiograph ; a, b, elastic tubing. I, III Vibra- 

 tion curves of a healthy person. IV Similar curve obtained from a patient 

 suffering from insufficiency of the aortic valves and great hypertrophy of the 

 heart. 



