Royal Society. 803 



maybe accomplished with facility after prolonged boiling), the aortic 

 aperture is separated from the left auricula-ventricular only by the 

 anterior mitral valve ; and when this is removed (or even while it re- 

 mains), it is plainly seen that only one aperture exists whose borders 

 are formed by the muscular tissue of the ventricle, and in shape 

 somewhat resembling the figure S. This is divided into two por- 

 tions, an anterior (aortic) and posterior (auriculo-ventricular) by the 

 anterior mitral valve, and above it, by the posterior wall of the aorta, 

 into which is inserted a large portion of the anterior wall of the left 

 auricle, but no muscular tissue of the ventricle intervenes. 



When the auricles and vessels are removed, it is seen that the 

 three orifices are bounded by thick and convex borders formed by 

 the bases of the ventricles. Those on the left side are broadest ; 

 the difference between the two sides corresponding with the differ- 

 ence in thickness between the walls of the ventricles. The forma- 

 tion of these muscular borders, and the general arrangement and 

 direction of the muscular fibres at these parts, are examined. The 

 fibres forming the walls of the ventricles converge around these 

 apertures. The most superficial fibres may be traced up from the 

 walls of the ventricles, curving obliquely over the convex border, 

 and having their extremities, for the most part, fixed arcund the 

 orifices. We may remove these fibres layer after layer, and still 

 find the same arrangement to obtain, the deeper fibres lying more 

 transversely and obliquely intersecting those above and below. 



If now the auricles and great vessels which have been detached are 

 replaced in their natural situation, it is observed that the auricles 

 are connected with the inner surface of these convex borders, while 

 the Avails of the vessels pass down on to the outer surface. This 

 fact is an important one when viewed in connection with the valves, 

 and will be presently considered. In the mean time it may be re- 

 marked, that the formation of the auriculo-ventricular grooves in 

 which the coronary vessels lie, is explained. These vessels are 

 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 artery. 



(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 with the yellow elastic tissue, 



Phil, Mug, S. 4. Vol. 3. No. 18. April 1852. X 



