148 



THE CIRCULATION OF THE BLOOD 



the base of the two ventricles in spiral bands toward the apex. These bands 

 of muscle are wound about the surface of the ventricles in the right-to-left 

 direction. At the apex they extend up into the deeper tissue. If the super- 

 ficial muscles are dissected off, there is left a great central core of muscle, 



FIG. 142. 



FIG. 143- 



FIG. 142. Diagram of the Course of the Layer Superficial to the Deepest Layer of the Muscle 

 of the Left Ventricle, which is shown in outline. The deepest layer is also shown. (After Mac- 

 Callum.) A, Posterior papillary muscle; B, papillary muscle of the septum. 



FIG. 143. Diagram of a Layer still more Superficial to that Shown in Fig. 142, and Ending 

 in the Anterior Papillary Muscle. The deeper layers are represented in dotted lines. (After 

 MacCallum.) A, Posterior papillary muscle; B, papillary muscle of septum; C, anterior papillary 

 muscle. 



which is described by MacCallum as running more transversely around the 

 wall of one ventricle, then through the septum and around the other in a 

 reverse scroll, figure 142. 



The Valves of the Heart. The valves of the heart are arranged 

 so that the blood can pass only in one direction. These are the tricuspid 

 valve, between the right auricle and right ventricle, figure 135, and the semi- 

 lunar valves of the pulmonary artery, the mitral valve between the left auricle 

 and ventricle, and semilunar valves of the aorta. The bases of the tricuspid, 

 figure 152, and mitral valves are attached to the walls of the auriculo-ven- 

 tricular rings, respectively. Their ventricular surfaces and borders are 

 fastened by slender tendinous fibers, the chorda tendinece, to the internal 

 surface of the walls of the ventricles at points which project into the ventricu- 

 lar cavity in the form of bundles or columns, the columns carnece. 



The semilunar valves guard the orifices of the pulmonary artery and of 

 the aorta. They are nearly alike on both sides of the heart, but the aortic 

 valves are altogether thicker. Each valve consists of three parts which are 

 of semilunar shape, the convex margin of each being attached to a fibrous 

 ring at the place of junction of the artery to the ventricle, and the concave 

 or nearly straight border being free, so as to form a little pouch like a pocket, 

 7, figure 136. In the center of each free edge of the valves which contains 

 a fine cord of fibrous tissue, is a small fibrous nodule, the corpus Arantii. 



