IO6 TOPOGRAPHIC AND APPLIED ANATOMY. 



PLATE 9. 

 An anterior view of the heart; the parietal pericardium has been incised and reflected. ( Formalin preparation.) 



organ in such a manner that two-thirds of the heart are upon the left side of the body and one- 

 third is upon the right. 



3. The apex of the heart touches the inner surface of the anterior thoracic wall and the 

 base approaches the vertebral column. The anterior surface of the heart is consequently also 

 directed upward and the posterior surface rests upon the diaphragm. 



Clearly note that after these three deviations of the cardiac axis from the position originally 

 assumed, the cardiac septum is still at right angles (but not in the sagittal plane) to the front- 

 plane of the body, and that equal portions of the right and left sides of the heart would be visible 

 from in front. 



4. The heart is now rotated upon its axis in such a manner that the greater portion of the 

 right heart is directed anteriorly (and superiorly) while the greater portion of the left heart is 

 situated posteriorly (and inferiorly). As a result of this rotation the cardiac septum is no longer 

 at right angles to the frontal plane, but lies more nearly in the frontal plane itself, as is best shown 

 in frozen sections (Fig. 50). 



It follows that the auricles at the base of the heart are situated superiorly and nearer to 

 the dorsal surface, while the ventricles are nearer to the thoracic wall. Injuries of the ventricles 

 are consequently comparatively more frequent than injuries of the auricles. As a further con- 

 sequence of the position of the heart, a horizontal penetrating wound may enter the ventricle 

 anteriorly and the auricle posteriorly. Since the ventricles are in contact with the inner sur- 

 face of the thoracic wall, their pulsations may be felt in the epigastrium (beneath the xiphoid 

 process), when there is marked cardiac hypertrophy. The right ventricle is the most anterior 

 portion of the heart, the right auricle is directed toward the right, the left ventricle toward the 

 left, and the left auricle is quite posterior (Fig. 50). In looking at the heart from in front, the 

 following structures are visible (Plates 9 and 16): the right ventricle with the origin of the pul- 

 monary artery (comes arteriosus), a narrow zone of the left ventricle, the anterior extremity of 

 the left auricular appendix, a goodly portion of the right auricle, and the right auricular appendix. 

 Each auricular appendix is situated over the arterial trunk originating from the opposite ventricle. 



In examining an excised heart the various structures may be best located by looking first 

 at the anterior surface of the viscus. 



At the inner surface of the anterior thoracic wall the largest portion of the heart is covered 

 by the two. anterior pulmonary margins. As they are air-containing structures they partially 

 mask the dull note obtained by percussion over this portion of the cardiac area (deep cardiac 

 dulness). A small portion of the heart lies directly against the inner surface of the thoracic 

 wall and is not covered by pulmonary tissue; over this area the trained ear recognizes the so- 

 called absolute cardiac dulness upon percussion. It is clear that this area must be diminished 

 when the lungs are distended (by emphysema, for example), and that it will be increased when 

 the edges of the lungs are drawn or pushed to one side (by a hypertrophied heart, for example) 

 (see Fig. 50). It is consequently important for the physician to be acquainted with the normal 



