BONE IN THE HEART OF MOOSE—SOMERS. ree 
the aorta into the left ventricle, as shown by Mr. J. W. Kina’s 
essay on the safety valve action of the right ventricle of the 
human heart. (Guy's Hosp. Reports, 1837. Vol. 11, p. 104.) 
Following the systole or contraction of the ventricles, the 
mass of blood which had been in their cavities is now in the 
aorta and pulmonary artery; distending them, the distension of 
the arterial walls is followed by their recoil. This would drive it 
back again into the ventricles, were it not for the sudden closure 
or shutting back of the pulmonic and aortic semi-lunar valves. 
The pressure which these valves have to bear is very consider- 
able, equalling that of 6 or 7 inches of mercury in man, and of 
course a still greater pressure in large animals. In regard to the 
action of the left side of the heart, the needs of the circulation 
demand that there shall be no regurgitation or backward flow of 
the blood. It must go forward, otherwise there is produced 
serious injury to the capillaries of the lungs and to the 
systemic circulation, a fact well known to pathologists, as in 
eases of insufficiency or obstruction in openings of the heart 
in man. 
In large animals, more especially those that are required to 
put forth efforts of strength or speed, which rapidly increase 
the blood pressure in the whole vascular system, the increased 
power of resisting pressure afforded by the partial bony ring at 
the aortic orifice must be of great consequence, so far as the 
specific functions of the semi-lunar valves here situated are 
concerned. It must be observed, also, that the bony matter but 
partly surrounds the aortic orifice, thereby while giving it 
strength and resisting power, not interfering with the necessary 
elasticity of the part. More than this, the solid tissue here in 
the cardiac septum affords more or less resistancy to the valves 
in the right side of the heart, preventing, during rapid or forced 
muscular action, the crowding of too much blood upon the deli- 
cate tissue of the lungs. 
In the various examinations of hearts which I have made, I 
have not found the second bone mentioned by OWEN and others. 
