THE HEART. 325 



into a right and left portion by a furrow, in which are the 

 arteries and veins of the heart, and corresponding to the 

 position of the external septum or dividing wall, which com- 

 pletely separates the right from the left cardiac cavities. The 

 explanations to the above cuts will furnish the reader with 

 the names of the parts represented, and it will be found that 

 c and d are the right and left auricles, which are situated at 

 the base of the heart, and separated by a circular furrow from 

 the right and left ventricles, a and b. 



The auricles, so called from the projection on which the 

 letter d is marked in Fig. 110, and which has been compared 

 to the flapping ears of a dog, receive the blood from the veins, 

 and constitute the venous portion of the heart,. whereas the 

 ventricular section is also termed the arterial, from its con- 

 nection with the pulmonary artery and aorta. 



If a section of the heart is examined, it is found that the 

 auricles and ventricles communicate freely, and the auriculo- 

 ventricular openings are provided in the left side with a two- 

 flapped valve, which has been compared to a bishop's mitre, 

 hence termed mitral, and in the right side the valve is three- 

 flapped or tricuspid. The flaps which form these valves are 

 connected with a tendinous ring between the auricles and 

 ventricles. This ring is partly cartilaginous in the horse, 

 and in the ox it contains bone. 



Fig. 112. ;LEYH.) Bone of the ox's heart, natural size, a, The anterior angle; 6 6, 

 the posterior angles; c, the upper border; d, the lower border; e, the posterior border; 

 /, the right surface. 



