178 



Heart. 



Y.coronaria 



520. Horizontal Section through the Heart 



(Vertically to the long axis of the body.) 



The heart is divided by a muscular septum into two halves, each 

 of which is again subdivided into an upper cavity, the auricle*, Auri- 

 cula, and a lower cavity, the ventricle, Ventriculus. The partition 

 between the ventricles is called Septum vcntrlculorum, that between the 

 auricles, Septum auriculorum. Each ventricle is triangular in form, the 

 walls of the left considerably thicker than those of the right. The mus- 

 cular columns, which project from nearly the whole of the inner surfaces 

 of the ventricles, are called Columnar carneae those which run across 

 the inner surface of the Appendix auriculae, and adjoining portion of the 

 wall of the sinus, Musculi pectinati. 



Into the right auricle the Venae cavae and coronary sinus open, 

 into the left the four pulmonary veins. Each auricle communicates with 

 the corresponding ventricle by means of the au.riculo-ventricu.lar 

 orifice, Ostiiun auriculo-ventriculare s. venosum ; the ventricles open into 

 the arteries which arise from them, each by means of an Ostium arteriosum, 

 the right into the pulmonary artery by means of the opening for the pul- 

 monary artery, the left into the aorta, by means of the aortic opening. All 

 openings have valves; between auricles and ventricles are the Valvulae auri- 

 culo-ventriculares, between ventricles and arteries the Vali'iilae semicircular -es. 



* The principal cavity or sinus of the auricle is often known as the atrium, to dis- 

 tinguish it from the auricular appendix, which is called auricle proper, Aitricuhi. 



