134 



found in the angle between the border of the ventricles and the wall 

 of the auricles. 



The nature of the fibrous zones or tendinous circles surrounding 

 the orifices is examined. These rings are in especial relation with 

 the valves, being closely connected with their attached bases, and 

 are not such distinct and independent structures as they have been 

 hitherto considered. After referring to some previous descriptions 

 of the arterial tendinous rings, the author attempts to show that 

 what has been described as the upper and thickened festooned border, 

 is the result of the attachment of the bases of the valves to the arte- 

 rial coat, and is formed by an intimate union of the fibrous tissue 

 composing the valves with the elastic coat of the arteryc 



(1) These festooned borders correspond exactly with the attached 

 bases of the valves, and hence their shape. (2) They are thickest and 

 most strongly marked at the angle formed by the junction of two 

 valves, to which point the bands of fibrous tissue in the valves con- 

 verge. (3) The microscope shows these festooned rings to be com.- 

 posed of a mixture of the white fibrous v^^ith the yellow elastic tissue, 

 an arrangement naturally to be expected from an intimate union of 

 the tendinous tissue of the valve with the arterial coat. 



The structure, connections and relations of the valves is examined 

 chiefly by means of vertical sections carried through their centres 

 and adjacent parts. Such sections of the arterial valves disclose an 

 important relation which they have with the upper border of the 

 ventricles. The aorta and pulmonary artery, expanding towards 

 their termination, are situated upon the outer edge of the ventricular 

 border before described ; the consequence of which arrangement is, 

 that the portion of valve adjacent to the vessel passes over and rests 

 upon the muscular substance, and is supported upon the inner border of 

 the free edge of the ventricles surrounding the arterial orifices. This 

 arrangement, in consequence of the small size of the parts, is not so 

 obvious at the first glance in the human heart, but is more strikingly 

 shown in an examination of the heart of any one of the larger 

 animals. This appears of importance when viewed in connection 

 with the functions of the valves. The reflux of the blood is said to 

 be sustained by the festooned rings at the base of the valves, but in 

 fact they are thinnest at this very part, corresponding to the central 

 portion of the convexity of the valves ; and if the description pre- 

 viously given of the formation of the tendinous festooned rings be a 

 correct one, it is obvious why it is so, the thicker portions being the 

 projecting angle at the junction of two valves, to which points the 

 tendinous fibres of the valves converge. Now, inasmuch as the pos- 

 terior portion of the aortic orifice is continuous with the left auri- 

 culo-ventricular aperture, no muscular tissue of the ventricle existing 

 at this part, the posterior aortic valve, and a portion of the adjacent 

 one, have no support of this kind ; but the muscular floor of the an- 

 terior aortic valve is especially broad, and it is the corresponding 

 portion of the aorta which is particularly dilated, the posterior wall 

 descending nearly vertically. The arrangement above described ob- 

 tains in all three pulmonary valves ; but as the border as well as the 



