THE HEART 



985 



The Position of the Chief Ohifices one to the othkr and 

 TO THE Chest Wall 



The pulmonary orifice is })la((Ml in front of, and to the k-ft of tlie ri«.dit auriculo- 

 vcntri(*ul;ir ()[>(nin^, whilst tiu- aortic orifice is in front of, and to the right of the 

 h'ft uuiiculo-ventricular o})ening. The rehition of the valved orifices to the chest 

 wall can only 1)C a])i)roxiniately determined (Fig. 547). 



The pulmonary semilunar valves, wliich are anterior in position to the aortic, 

 are placed l)ehind the junction of the third rib with tlie sternimi on the left side. 



Fig. 554.— Showing the Position of the Heart and its Valves in Relation to the 



Chest Walls. 



(Reduced from Hensman and Fisher's Anatomical Outlines.) 



(The right auricle ami ventricle, with the pulmonary semilunar and tricusipid valves, are outlined in blue tints; 

 whilst the left auricle and ventricle, with their corresponding valves, are indicated in red.) 



The aortic semilunar valves, more deeply placed, correspond to the third 

 space, close to the sternum. 



The tricuspid valve is situated Inhind the strrnum m-ar the middle line, ahout 

 the level of the fourth s))ace. 



The mitral valve lies deeply behind the sternum o})posite the fourth cartilage 

 ( Fig. 547 ). 



The muscular walls of the heart vary very much in thickness, and tlie fotal 

 differs from the adult heart in the relative muscularity of its chambers. 



The right auricle is thinner than the left, the right measuring about one-twelfth 

 of an inch, and the left abf)Ut one-eighth of an inch in thickness. The right ven- 



