320 DETAILED SYNTHESIS. 



surface is rubbed, the outward movement should be made with gentle 

 pressure, and that toward the centre of the body with vigor. 



902. THE VEINS EXTEND FROM THE CAPILLARIES of 

 the body toward the chest in two courses, one near the 

 surface, and another deep, near the arteries, most of 

 which have a vein on each side. These two courses fre- 

 quently communicate, both directly and indirectly. In 

 both courses, but particularly in the superficial one, the 

 veins unite nearly at right angles, as seen on the back 

 of the hand. They at last unite at the auricles of the 

 heart, into which they pour the Blood drained from 

 every part of the body. 



903. THE USE OF THE VEINS is merely that of passive 

 strong tubes, allowing the flow of Blood from one part 

 of the body to another. The force of its flow through 

 the veins is derived from or through the capillaries, the 

 action of the muscles about them, and temporary pres- 

 sure upon the surface of the body. 



904. Inf. Rubbing the surface must promote circulation of Blood 

 in veins. 



905. VEINS ARE CONSTRUCTED OF THREE TISSUES, a 

 framework of sinewy, a lining of secretory, and a little 

 muscular. 



Hearts. 



906. HEARTS MAY BE CONSIDERED as merely veins, 

 with walls thickened with muscular tissue ; for, if in the 

 walls of a, Fig. 207, considerable muscular tissue should 

 be introduced, a heart would be constructed. 



907. Remark. The form of the heart is not an essential point, a 

 muscular pouch of any form, with valves at its two openings, allowing 

 the Blood to move in only one direction, is all that is necessary. Hearts 

 like that suggested in the preceding paragraph exist in some animals, 

 and the human heart is the same in general principles, its modifications 

 adapting it to its peculiar offices. 



902. How do ? 903. What is ? 904. Effect of rubbing. 90& Of what - f 

 906. How may ? 907. Is form essential in the heart? 



