Elementary Anatomy of a Hound 39 



one or two exceptions to this have been known in 

 man, when power to inhibit or control this vital organ 

 has been demonstrated. Perhaps one of the most 

 significant features of the minute muscular fibres 

 composing the heart is the junction of one fibre with 

 another, whilst the fibres of the upper and lower 

 compartments are separated from each other. 



The heart has four compartments, viz., a right and 

 left auricle above and a right and left ventricle below, 

 with valves for regulating the flow of blood to and 

 from these compartments. The auricles or upper 

 compartments help to form the base of the heart, 

 whilst its apex — directed in a downward and back- 

 ward direction — is formed by the muscular substance 

 of the heart, the left ventricle extending down to the 

 apex. The wall of this compartment is much thicker 

 than that of the right side, because when it contracts it 

 has to send the stream of blood (per a blood-vessel 

 coming from it and called the aorta) throughout the 

 system — the systemic circulation, as opposed to the 

 lesser or pulmonary circulation, propelled to the lungs 

 by the right ventricle, through the pulmonary artery 

 (carrying impure blood — an exception to arteries). 

 The valve guarding the opening between the auricle 

 and ventricle on the left side has two cords of attach- 

 ment, hence it is called the bicuspid valve, whilst 

 that on the right side has three cords of attachment. 



This is the tricuspid valve. The cusps or flaps 



