476 STRUCTURE OF THE HEART. 



in length towards the base. Its walls are about seven lines in thick- 

 ' ness, those of the right ventricle being about two lines and a half. 



It presents for examination, in its interior, two openings, two 

 valves, and the tendinous cords and muscular columns ; they may 

 be thus arranged : 



Auriculo-ventricular opening, 

 Aortic opening. 



Mitral valves, 

 Semilunar valves. 



Chorda? tendinese, 

 Columnar carnece. 



The Auriculo-ventricular opening is a dense fibrous ring, covered 

 by the lining membrane of the heart, but smaller in size than that of 

 the right side. 



The Mitral valves are attached around the auriculo-ventricular 

 opening, as are the tricuspid in the right ventricle. They are thicker 

 than the tricuspid, and consist of only two segments, of which the 

 larger is placed between the auriculo-ventricular opening and the 

 commencement of the- aorta, and acts the part of a valve to that 

 foramen, during the filling of the ventricle. The difference in size 

 of the two valves, both being triangular, and the space between 

 them, has given rise to the idea of a " bishop's mitre" after which 

 they are named. These valves, like the tricuspid, are furnished 

 with an apparatus of tendinous cords, chwda tendinece, which are 

 attached to two very large columna carnece. 



The Columnar car-neat admit of the same arrangement into three 

 kinds, as on the right side. Those which are free by one extremity, 

 the columnse papillares, are only two in number, and much larger 

 than those on the opposite side. 



The Semilunar valves are placed around the commencement of 

 the aorta, like those of the pulmonary artery ; they are similar in 

 structure, and are attached to the scalloped border by which the 

 aorta is connected with the ventricle. The tubercle in the centre 

 of each fold is larger than those in the pulmonary valves, and it was 

 these that Arantius particularly described ; but the term " corpora 

 Jlrantii" is now applied indiscriminately to both. The fossa? between 

 the semilunar valves and the cylinder of the artery are much larger 

 than those of the pulmonary- artery ; they are called the " sinus 

 aortici" 



STRUCTURE OF THE HEART. 



The arrangement of the fibres of the heart has been made the 

 subject of careful and accurate investigation by Mr. Searle, to 

 whose excellent article, " Fibres of the Heart," in the Cyclopaedia 

 of Anatomy and Physiology, I am indebted for the following sum- 

 mary of their distribution : 



