* AN ANATOMICAL STUDY ON THE 



bulge outward, the cavities dilate, the ventricles 

 take the shape of cupping glasses, and suck the 

 blood into them. But all the fibers constrict the 

 heart at the same time that they make it tense, thus 

 thickening the walls and substance rather than 

 enlarging the ventricles. As the fibers stretch from 

 the apex to the base of the heart, drawing the apex 

 toward the base, they do not tend to make the walls 

 bulge outwards, but rather the reverse, for all fibers 

 spirally arranged become straight on contraction. 

 This is true of all muscular fibers. When they con- 

 tract they shorten longitudinally and distend side- 

 wise as they thicken, as noted in the bellies of 

 muscles generally. To this may be added that the 

 ventricles are not constricted only by virtue of the 

 direction and thickening of their walls. The walls 

 contain solely circular fibers, but there are also 

 bands containing only straight fibers, which are 

 noted in the ventricles of larger animals and which 

 are called nerves by Aristotle.^ When they contract 

 together an excellent system is present to pull the 

 internal surfaces closely together, as with cords, in 

 order to eject the blood with greater force. 



^ The inside walls of the ventricles are ridged with many projecting 

 bands of muscle tissue, arranged as (i) separate threads stretched 

 across the cavity, the moderator bands especially noted in the right 

 ventricle; (2) columns on the walls, the columnae carmae, which are 

 probably referred to here, and (3) small elevations on the walls, 

 papillary muscles^ which are prolonged in the chordae tendineae extend- 

 ing to the valves. The latter probably aid inclosing more exactly the 

 valve flaps. See R. Burton-Opitz's Physiology, Phila. and London, 

 1920, p. 267-270. Harvey discusses these "bands" again in Chapter 

 XVII. 



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