. The structure and life of birds . he upper. In the bird this valve is simply a flapof muscle which projects into the ventricle, and whichcloses the aperture when it is lifted by a rush of bloodupwards. In man and other mammals the valve isformed of thin membrane instead of muscle, andconsists of three flaps connected with one another andfastened by strings of tendon to the walls of the heartbelow. This is called the tricuspid valve. It is verycurious that the birds heart should be in most respectsso similar to that of man, in this respect so valves remain to show that the two
. The structure and life of birds . he upper. In the bird this valve is simply a flapof muscle which projects into the ventricle, and whichcloses the aperture when it is lifted by a rush of bloodupwards. In man and other mammals the valve isformed of thin membrane instead of muscle, andconsists of three flaps connected with one another andfastened by strings of tendon to the walls of the heartbelow. This is called the tricuspid valve. It is verycurious that the birds heart should be in most respectsso similar to that of man, in this respect so valves remain to show that the two highest VI FORM AND FUNCTION 73 classes of animals, mammals and birds, have eachseparately developed a perfect type of heart fromsome lower form which allowed the pure and impureblood to mix. On the left side of the heart also thepassage between the upper and lower cavities isguarded by a valve. Both in birds and mammals itis formed of two membranous flaps fastened to thewalls below by strong cords of the nature of tendons. ■ M^. TV -
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Keywords: ., bookcentury1800, bookdecade1890, bookidstructurelif, bookyear1895
