356 A MANUAL OF ANATOMY. 



only of the two layers of the endothelium of the vessel. 

 These thin places admit of a closer apposition of the valves. 



The sinuses of Valsalva are hollows behind each cusp 

 of the semilunar valves (whether in pulmonary artery or the 

 aorta). 



The sinuses are arranged in the pulmonary artery with 

 two in front (the left is slightly in front of the right) and 

 one in the rear. 



In the aorta these sinuses are arranged with one in front 

 and two behind. See Coronary Arteries, pages 352 and 353. 



The inner surface of the ventricle is corrugated by mus- 

 cular ridges, the columnae carneae. These are found in 

 three forms : one, attached by their whole lengths ; a second, 

 by both ends ; a third, by one end (musculi papillares), 

 the other end being free and affording attachment to the 

 chordae tendineae. The chordae tendinese are fibrous 

 strings passing from the musculi papillares to the under 

 surface and free borders of the primary and secondary por- 

 tions of the tricuspid (and bicuspid) valve. 



The Left Ventricle. This ventricle is about three times 

 thicker than the right one. From it extends the aorta, and 

 into it empties the left auricle through the auriculoventri- 

 cular opening. The aortic opening is provided with semi- 

 lunar valves and the auriculoventricular with the bicuspid 

 (mitral) valve, similar in every way to the semilunar and 

 tricuspid of the right ventricle. 



The auriculoventricular or bicuspid valve is com- 

 posed of two main and two secondary flaps. Behind the 

 semilunar valves the aortic wall is pouched ; these pouches 

 are called the sinuses of Valsalva, as above described. 



The Trachea. Figs. 18, 70, 71, 72. Diags. 20, 21. 

 The trachea is a fibromuscular tube that is prevented 



