78 ' DISEASES OF CATTLE. 



The communication between the auricle and ventricle of either side is 

 called the auriculo-ventricular opening, and both orifices are regulated 

 by valves. The compartments of the heart are manifest on its outer 

 surface by grooves or furrows. There is a transverse groove which 

 marks the division between the auricular and ventricular parts. This 

 groove also marks the location of the auriculo-ventricular openings on 

 the inside. The upper portion of the heart is constricted in the middle 

 of its superior face; the section on either side of the constriction repre- 

 sents one of the auricles. Into the right section are inserted the pos- 

 terior vena cava, the anterior vena cava, the vena azygos, and coronary 

 vein. Into the left section are inserted the pulmonary veins, usually 

 four in number. The ventricular portion includes all that is below the 

 transverse groove; it is much the greater portion of the organ and gives 

 to it the shape of a cone or pyramid. On either face is seen a groove 

 which marks the division between the right and left ventricle. In 

 cattle an accessory groove runs down behind the left ventricle. All 

 the grooves are occupied by blood-vessels and fatty tissue. The com- 

 mon aorta and the pulmonary artery leave the upper portion of the 

 ventricular mass on the left of the anterior part. 



The cavities of the heart are designated as the right and left, and 

 there is no communication between the right and left cavities after the 

 birth of the young animal. During the life of the fetus in the womb 

 there is an opening in the wall between the right and left auricles 

 called the foramen ovale, but at birth this is closed, and there remains 

 only a depression in the wall to mark the place where it existed. It 

 occasionally happens that the foramen ovale remains open after birth, 

 and this exception will be referred to hereafter under the head of 

 Cyanosis. In the cavities are to be seen the orifices of the vessels 

 (through which the blood enters and leaves the heart), the names of 

 which have been given. 



At the bottom of each auricle is the auriculo-ventricular opening; 

 each opening is provided with a valve to close it when the heart con- 

 tracts to force the blood into the arteries. In the interval between the 

 contractions these valves hang down into the ventricles. Little ten- 

 dinous cords stretching from the free edges of the valves to the walls 

 of the ventricles prevent the blood from forcing the valves too far up 

 into the auricles during contraction of the heart, which prevents the 

 return of blood into the auricles. 



The opening of the common aorta and pulmonary artery and the 

 ivuriculo- ventricular openings are surrounded bj' rings of fibrous tissue 

 which form the frame on which the muscular tissue of the heart rests. 

 In cattle there are found two small bones in the fibrous tissue of the 

 ring of the common aorta. The fibrous tissue completely surrounds 

 the openings of the aorta and pulmonary artery, but the rings around 

 the auriculo- ventricular openings are incomplete. 



The muscular tissue of the heart belongs to that class known as in- 



