THE VALVES OF THE HEART 45 



striated, like the substance of a striated fibre. A number 

 of such cells are j-ined by cement substance mto sets of 

 anastomosing fibres, which are built up in a complex mter- 

 woven manner into the walls <.f the ventricles and auricles. 

 The cavities of the heart are lined by a smooth, shmy 

 membrane called the endocardiTim, which consists of a 

 layer of connective tissue covered with thin flattened cells 

 continuous ^^ ith and simUar to those which form the waU 

 of the capillaries and which line the arteries and veins. 

 At the junction between the auricles and ventricles, 

 the apertures of c<jmmunication between theii" cavities, 

 caUed the auriculo-ventricular apertures, are 

 strengthened bv fibrous rings of connective tissue. To 

 these" rings the movable partitions, or valves, between 

 the auricfes and ventricles, the arrangement of which 

 must next be c«>nsidered. are attached. 



5. The Valves of the Heart.— There are three of 

 these partitions attached to the circumference of the right 

 auriculo-ventricular aperture, and two to that of the left 

 (Figs. 16, 17, 18, 19, t r, m t). Each is a broad, thm, but 

 very tough and strong triangular fold of connective tissue 

 (see Lesson XII.) covered by endocardium, attached by 

 its base, which joins on to its fellow, to the auriculo- 

 ventricular fibrous ring, and hanging with its point 

 domiwards into the ventricular cavity. On the right 

 side there are, therefore, three of these broad, pointed 

 membranes, whence the whole apparatus is called the 

 tricuspid valve. On the left .side, there are but two, 

 which, when detached from aU their connexions but the 

 auriculo-ventricular ring, l(»ok something like a bishop's 

 mitre, and hence bear the name of the mitral 



valve. 



The edges and apices of the valves are not completely 

 free and loose. On the contrary, a number of fine, but 

 strong, tendinous cords, called chordae tendineae, con- 

 nect them with some column-like elevations of the fleshy 

 substance of the walls of the ventricle, wliich are termed 



