THE BLOOD-VASCULAR SYSTEM OF THE OX 705 



ried into the right atrium by the posterior vena cava passes largely, if not entirely, 

 through the foramen ovale into the left atrium, while the blood flowing into it 

 through the anterior vena cava passes into the right ventricle. On this basis the 

 blood received by the left atrium consists chiefly of mixed blood from the posterior 

 vena cava, since the small amount of blood conveyed by the pulmonary veins is 

 venous. This mixed blood passes into the left ventricle and is forced into the 

 systemic arteries. The venous blood from the anterior part of the body and the 

 thoracic limbs is conveyed by the anterior vena cava to the right atrium, passes 

 into the right ventricle, and is forced into the pulmonary artery. A small amount 

 is carried to the lungs, but the bulk of it passes by the ductus arteriosus into the 

 aorta behind the point of origin of the brachiocephalic trunk, and is carried to the 

 posterior part of the body, a large part passing by the umbilical arteries to the 

 placenta. 



THE BLOOD-VASCULAR SYSTEM OF THE OX 

 The Pericardium and Heart 



The pericardium is attached to the sternum opposite the facets for the sixth 

 costal cartilages by two fibrous bands, the sterno-pericardiac ligaments (Ligg. 

 sternopericardiaca) ; these ligaments, right and left, are embedded in the mass of fat 

 which separates the apex of the pericardium from the floor of the thorax. On the 

 left side the greater part of the pericardium is in contact with the chest wall as far 

 back as the fourth intercostal space. On the right side the pericardium is com- 

 monly covered by the lung, and has therefore no contact with the lateral chest wall. 

 But in some cases there is a small cardiac notch on the right lung opposite to the 

 ventral part of the third rib and intercostal space. 



The heart of the adult ox has an average weight of about five and a^alf pounds 

 (ca. 2.5 kg.), or about 0.4 to 0.5 per cent, of the body-weight. Its length from base 

 to apex is relatively longer than that of the horse, and the base is smaller in both 

 its diameters. The ventricular part is more regularly conical and more pointed. 

 A shallow intermediate groove (Sulcus intermedius) extends from the coronary 

 groove down the left side of the posterior border, but does not reach the apex. The 

 amount of fat in and near the grooves is much greater than in the horse. Even 

 more of the heart is situated to the left of the median plane than in the horse. The 

 base is opposite the chest wall from the third rib to the fifth intercostal space, both 

 inclusive. The apex is opposite to the fifth interchondral space; it is just to the 

 left of the median plane, and is about an inch (ca. 2.5 cm.) from the diaphragm. 

 The long axis is much less oblique than in the horse. The posterior border is 

 opposite to the fifth intercostal space; it is practically vertical and is slightly con- 

 cave. 



The pulmonary orifice is opposite to the third rib in part and the third intercostal space, 

 about a handbreadth (ca. 10-12 cm.) above the sternal ends of the ribs. The aortic orifice is 

 chiefly opposite to the fourth rib. The right atrio-ventrioular orifice is opposite to the third inter- 

 costal space and fourth rib and space. The left atrio-ventricular orifice is chiefly opposite to the 

 fourth intercostal space and fifth rib. 



The left longitudinal groove corresponds to the fourth rib. The right groove is chiefly pos- 

 terior; it begins below the termination of the posterior vena cava. The intermediate groove 

 begins below the posterior end of the left auricle, and in its descent inclines gradually to the left 

 side of the apex. 



The vena hemiazygos usually unites with the terminal part of the great cardiac 

 vein, thus forming a trunk which opens into the right atrium below the posterior 

 vena cava. 



Two bones, the ossa cordis, develop in the aortic fibrous ring. The right one 

 45 



