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walls of the right ventricle are considerably thinner than those of the 

 left, the muscular floor of these valves is much narrower than in 

 the anterior aortic valve. All this is of course seen on a much 

 larger scale in the hearts of the larger animals, as the Horse and 

 Ox ; and here, where the muscular floor of the valves (more espe- 

 cially the anterior aortic) is of very considerable breadth, the ten-, 

 dinous tissue of the valve may be traced over the muscular surface 

 to form the wall of the vessel. 



In the larger Ruminants there are found two considerable por- 

 tions of bone, partly surrounding the orifice of the aorta, and smaller 

 irregular fragments are occasionally observed between the principal 

 pieces. The larger portions vary much in size and shape in difi'erent 

 hearts even of the same species. They are usually elongated and 

 curved. The chief bone, which exceeds the other considerably in 

 size, embraces the whole of the right side, and the right half of the 

 back part of the orifice of the aorta ; while the little bone, not gene- 

 rally found in the smaller Ruminants, as the Sheep, its place being 

 occupied by a portion of dense fibrous tissue, extends from the middle 

 of the left side round to the posterior part, w^here it more or less 

 nearly joins the extremity of the larger bone. Thus the lateral and 

 posterior portions of the aortic orifice are surrounded by firm bony 

 arches meeting posteriorly in the centre. From the large bone, a 

 small process usually passes backwards for some distance into the 

 muscular substance of the septum between the ventricles, and is 

 gradually lost in the dense fibrous tissue found in this part, sur- 

 rounding the right border of the left auriculo-ventricular aperture ; 

 and from the convex surface of the smaller portion, a thin process of 

 dense fibrous tissue is continued round the left margins of the auri- 

 culo-ventricular orifice. These heart-bones are intimately connected 

 above with the middle coat of the aorta, on the inner surface with 

 the base of the adjacent arterial valves, and posteriorly with the an- 

 terior mitral valve ; while at the sides, to their external and inferior 

 surfaces, the muscular fibres of the ventricle are attached. They 

 may be seen and felt in the base of the pouches formed by the two 

 posterior aortic valves, and no doubt greatly assist in sustaining the 

 " force°^of the reflux." They occupy the position of the two posterior 

 festoons of the aortic valves. In the human heart, in the situation, 

 corresponding to the position of these heart -bones, the tissue com- 

 posing the festooned rings is thicker and denser than elsewhere, 

 offering to the knife, in some cases, almost the resistance of bone. 

 The processes of dense fibrous tissue found in the anterior portion 

 of the border of the ventricular septum, &c., and extending round 

 the right and left margins of the auriculo-ventricular orifice, are in- 

 timately connected with the thickened portions of the adjacent 

 festoons. 



Among the tissues entering into the structure of the arterial valves, 

 elastic fibres are described. They exist not only in the corpus 

 arantii, but delicate fibres of elastic tissue are found throughout the 

 valve ; most abundantly in the thicker portions, but even in the 

 thinner portions (lunulee) a few delicate but well-marked elastic 



10* 



