PHYSIOLOGICAL ANATOMY OF THE HEART. 



33 



FIG. 12. Course of the muscular fibres of the left 

 auricle (Landois). 



one of which, the external, is common to both auricles, and the other, the 

 internal, is proper to each. These muscular fibres, although involuntary in 

 their action, belong to the striated variety, and are similar in structure to the 

 fibres of the ventricles. The fibres of the auricles are much fewer than those 

 of the ventricles. Some of them are 

 looped, arising from a cartilaginous 

 ring which separates the auricles and 

 ventricles and passing over the auri- 

 cles; and others are circular, sur- 

 rounding the auricular appendages 

 and the openings of the veins, ex- 

 tending, also, a short distance along 

 the course of these vessels. One or 

 two valvular folds are found at the 

 orifice of the coronary vein, prevent- 

 ing a reflux of blood, but there are no valves at the orifices of the venae cavae. 

 The left auricle receives the blood which comes from the lungs by the 



pulmonary veins. It does 

 not differ materially in its 

 anatomy from the right. 

 It is a little smaller, and 

 its walls are thicker, 

 measuring about a line 

 and a half (3-15 mm.). 

 It has four openings by 

 which it receives the 

 blood from the four pul- 

 monary veins. These 

 openings are not provid- 

 ed With valves. Like the 

 right auricle, it has a 

 large opening by which 

 blood flows into the cor- 

 responding ventricle. The 

 arrangement of the mus- 

 cular fibres is essentially 

 the same as in the right 

 auricle. In adult life, the 

 cavities of the auricles are 

 entirely distinct from each 

 other. Before birth, they 

 communicate by a large 

 opening, the foramen 



FIG. 13. Heart, anterior view (Bonamy and Beau). OVale, and the Orifice of 



1, right ventricle ; 2, left ventricle ; 3, 4, right auricle ; 5, 6, left au- ,1 in-fow^r VOTIQ vn i 



ride ; 7, pulmonary artery; 8, aorta; 9, superior vena caya ; 10, the mleiior Vena Ca\a IS 



anterior coronary artery ; 11, branch of the coronary vein ; 12, ^..^.^oH with a 



12, 12, lymphatic vessels. plOViaeQ Wltn a 



