THE HEART 307 



Patency of the ductus arteriosus may occur alone. In this 

 case much of the blood which was intended for the lungs is 

 carried off by the ductus into the aortic system, so that there 

 is diminished oxygenation, and, as a result, well-marked 

 cyanosis is present. A loud bruit, systolic in time, is heard 

 all over the praecordia, but its point of maximum intensity is 

 situated behind the left half of the sternum opposite the second 

 intercostal space, i.e. over the pulmonary artery. The condi- 

 tion may be distinguished from acquired aortic stenosis by the 

 complete absence of any enlargement of the left ventricle. 



Congenital anomalies of the cardiac valves occur with much 

 greater frequency on the right than on the left side of the heart, 

 and the cusps of the semilunar valves are more commonly 

 affected than those of the tricuspid valve. The cusps may be 

 increased to four or five in number or decreased to two, but 

 the condition is of no moment unless accompanied by stenosis 

 of the pulmonary orifice. The latter condition is the com- 

 monest variety of congenital heart lesion which is met with in 

 practice, and it is marked by three cardinal signs (a) Cyanosis ; 

 (b) a loud systolic murmur with a weak second sound in the 

 pulmonary area; (c) enlargement of the right side of the 

 heart. In many of these cases, the diminished flow of blood 

 to the lungs determines the onset of pulmonary tuberculosis. 



NERVE-SUPPLY OF THE HEART. The nerves which supply 

 the heart are derived from the sympathetic system and from 

 the vagi, through the superficial and deep cardiac plexuses. 

 The sympathetic nerves have their centres in the spinal 

 medulla in the upper four thoracic segments, and they pass 

 into the upper four thoracic ganglia of the sympathetic in the 

 white rami communicantes. They then ascend into the 

 cervical portion of the sympathetic trunk and are given off as 

 the cardiac branches of the cervical ganglia. The somewhat 

 circuitous course which these fibres take is explained by the 

 fact that, at the period when the heart receives its nerve- 

 supply, it is situated in the cervical region. 



The Superficial Cardiac Plexus is placed immediately below 



