REPAIR IN EVOLUTION 75 



blasts gradually become non-muscular. This must have 

 been originally a pathological process. It is a reversion, 

 a degeneration made use of. We observe analogous, or 

 shall I say homologous ? results in the hypertrophied heart. 

 The normal male heart weighs about eleven ounces. In 

 some cases of aortic stenosis it may weigh over thirty ounces. 

 In such hypertrophied muscle are often found fibrous 

 tissues which probably represent the connective tissue of 

 muscular fibres which have atrophied from overstrain. The 

 attachments of the mitral valve are less muscular and more 

 fibrous than those of the tricuspid. The greater elasticity 

 of the tricuspid papillares musculi and the annular muscles 

 of the base of the ventricle thus allows an overfull right 

 ventricle, which is so much less powerful than the left, 

 to be relieved by the temporary functional incompetence 

 of the tricuspid valve. In the reptile with a functioning 

 foramen the valves are purely mechanical, as pressure is 

 relieved by the patent orifice. The fossa ovalis in the 

 mammal is a remnant of the early communication between 

 the auricles. In a large number of normal hearts there is 

 a small valvular passage yet remaining in the left margin 

 of the fossa. None of these phenomena seem capable of 

 explanation as the result of spontaneous variations 

 arising from some theoretic instability of the organism. 

 To argue that they are is to give biologic mystics a chance. 

 It appears obvious from all these facts taken together 

 that cardiac evolution has been a series of caused varia- 

 tions due to increased and varying stresses, which acted 

 not only as a moulding force on the shape and musculature 

 of the heart, but on all its appendages. In the muscle of 

 the ventricular walls with its extraordinary complexity of 

 layers and interlaced fibres lies powerful evidence of such 

 reactions. In both ventricles there are seven muscular 



