CIRCULATORV SYSTEM. 175 



edges, three small granular substances, described as the corpus- 

 cuia Arantii. Opposite to the valves, three depressions are ap- 

 parent in the coats of the vessel, named the siuus Valsalvce. 



The left auricle is smaller than the right, and has thicker 

 parietes. It contains, in general, but little blood, and in some 

 subjects none. It presents nearly the same aspect internally as 

 the right. It has not so much of the reticulated structure how- 

 ever — (ewer muscu/i pectiuati ; what there are, are more strongly 

 marked, and are principally confined to the appendix. The p?//- 

 monary veins terminate by four openings in the superior and pos- 

 terior part of this cavity. The auriculo-ventrkular opening is 

 somewhat larger than that of the right side, and is rather square 

 than round. Now that the auricles are both laid open, the septum 

 auricularum, Jossa ovalis, and Jorame?i ovctle, may be distinctly 

 viewed. 



The left ventricle, though smaller within, is longer, and 

 more prominent and extensive without, than the right : it forms, of 

 itself, i\\eapex cordis. Its outer wall far exceeds in thickness that 

 of any other cavity of the heart, being thrice that of the right ven- 

 tricle. Its musculi pectinati appear mostly upon the septum, 

 within the apex, and under the valves. It has but two carnece 

 columncE, but they are very bulky, and project much into the 

 cavity. Its auriculo-ventricular opening is only furnished with 

 ^?^o valvular productions ; in other respects the cortina tendinea 

 and chordcc tendinea resemble those on the right side : this valve 

 is called the valvnla biciispis vel mitralis. The aorta takes its 

 rise from the upper and fore part of this ventricle, and, concealed 

 at its origin by the pulmonary artery on one side and venae cavae 

 on the other, makes its exit close to the spine. The mouth of the 

 aorta is shut by three semilunar valves, similar in formation and 

 disposition to those at the origin of the pulmonary artery : but the 

 sinus Valsalva are much larger and deeper. Just above two of 

 them are seen the mouths of the coronary arteries. The ventri- 

 cles are divided by a thick fleshy partition, called the septum ven- 

 triculorum. 



Organization. — Though the heart is composed mostly of fleshy 

 fibres, a tendinous structure is demonstrable in its middle, which 

 tendinous intertexture appears to be the common medium of at- 

 tachment between its auricles, ventricles, vessels, and valves, one to 

 another. The fleshy fibres composing the parietes of the auricles, 

 stronger in the left than in the right, are disposed in every direction; 

 those that form the walls of the ventricles, for the most part, appear 

 to run longitudinally and obliquely, and many of them in a spiral 

 manner. These fibres are more slender than those of other 



