THE CIRCULATION. 



223 



The left auricle has thick walls, and the walls are not so trans- 

 lucent as those of the right auricle. It has a smooth interior sur- 

 face, except with the auricular appendage, where pectinate muscles 

 are present. It has four openings, which are the pulmonary veins, 

 two in the right and two in. the left side of the auricle. At the 

 lower anterior part of the cavity is the left auriculo-ventricular 



Fig. 63. Heart of the Cow, with Left Auricle and Ventricle Laid 

 Open. (MilLLER.) 



a, Root of the aorta. 6, Spaces in the wall of the auricle, c, c, Orifices 

 of the pulmonary veins. I, I, Pulmonary -veins, p, p, Papillary muscles, q, q, 

 Columnae carneae. A, Orifice of the aorta. K, Left ventricle. S, Septum. F, 

 Left auricle. W, Lateral wall of left ventricle. 1, 1, 2, Leaflets of mitral valve. 



orifice. The right ventricle is in the shape of a pyramid with the 

 base upward and backward. It extends from the right auricle to 

 near the apex of the heart, and occupies more of the front surface 

 of the heart than the left ventricle. The walls of the right ven- 

 tricle are only one-third the thickness of those of the left. The 

 septum ventriculorum bulges into the right ventricle. There are 



