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 279 A N A T O M Y. Part VI. infide, but finoother on the outfide, and terminate The fieftiy or mufcular fibres of which the heart is on athenarrow, flat, indented edge, reprefenting a cock’s made up, are difpofed in a very Angular manner, efpe- incomb, in fome meafure the ear of a dog. They open cially thofe of the right or anterior ventricle, being either into thefeor orifices of each ventricle, which are named auribent into arches or folded into angles. orifices ; and they are tendinous at their opening, The fibres which are folded into angles are longer than cular thofe which are only bent itato arches. The middle of theie in the fame manner as the ventricles. right auricle is larger than the left, and it joins arches, and the angles of the folds, are turned towards theThe the apex of the heart, and the extremities of the fibres right ventricle by a common tendinous opening. It towards the bafis. Thefe fibres differ not only in length, has two other openings united into one, and formed bv large veins which meet and terminate there, almoll but in their dire&ions, which are very oblique in all, but intwoa direft line, called vena cava fuperior and inferior. much more fo in the long or folded fibres than in the The notched edge of this auricle terminates obliquely in (hort ones, which are fimply bent. Each ventricle is compofed of its proper diflinft fibres, a kind of obtufe point, which is a fmall particular producbut the left ventricle has many more than the right. tion of the great bag, and is turned towaid the middle Where the two ventricles are joined, they form a feptum of the bafis of the heart. The left auricle is a kind of mufcular bag or refervoir, which belongs equally to both. The fibres which compofe the inner or concave furface of a pretty confiderable tbicknefs, and unequally fquare, of the ventricles, do not all reach to the bafis ; fome of into which the four veins open, called venue pulntonares, them running into the cavity, and there forming the and which has a diftind appendix belonging to it, like a flefhy columnse, to which the loofe floating portion of third fmall auricle. This bag is very even on both fides. The heart lies almoft tranfverfely on the diaphragm, the tricufpidal valves is faftened by tendinous ropes. The valves at the orifices of the ventricles are of two the greatell part of it being in the left cavity of die thokinds. One kind allows the blood to enter the heart, and rax, and the apex being turned toward the bony extreof the fixth true rib. The bafis is toward the right hinders it from going out the fame way ; the other kind mity allows the blood to go out of the heart, but hinders it cavity; and both auricles, efpecially the right, reft cm from returning. The valves of the firft kind terminate the diaphragm. pf the great arteries. The firll are termed femulanarorfig- natural fituation, the .higheft part of the heart on the moidal valves, the others triglochines, tricufpidal, or mitral, forefide ; and the trunk of this artery lies in a perpendii The tricufpidal valves of the right ventricle are fixed cular plane, which may be conceived to pals between the to its auricular orifice, and turned inward toward the fternum and fpina dorfi. Therefore fome part of the cavity of the ventricle. They are three triangular pro- bafis of the heart is in the right cavity of the thorax; rfudions, very fmooth and polifhed on that fide which is and the reft, all the way to the apex, is in the left caturned towards the auricle; and on the fide next the ca- vity ; and it is for this reafon that the mediaftinum is vity of the ventricle, they have feveral membranous and turned toward that fide. tendinous expanfions, and their edges are notched or in- According to this true natural fitnation of the heart, dented., The valves of the auricular orifice of the left the parts commonly find to be on the right fide are raventricle ,are of the fame ftiape and ftrudture, but they ther anterior, and ^hqfe on the left fide pofterior; and are only two in number ; and from fome fmall refem- that fide of the heart which is thought to be the forefide, is naturally the upper fide, and the backfide confequentblance to a mitre, they have been named mitrales. The femilunar valves are fix in number, three belong- ly the lower fide. ing to each ventricle, fituated at the mouths of the great The lower fide is very flat, lying wholly on the diaarteries; and they may be properly enough named val- phragm ; but the upper fide is a little convex through its vuke arteriales. whole length, in the direftion of the feptum between the The great artery that goes out from the left ventricle, ventricles. is termed aorta. As it goes out, it turns a little toward The heart, with all the parts belonging, to it, is conth® right band, and then bends obliquely backward to tained in a membranous capfula, called pericardium, form what is called aorta defcendens. which is in fome meaiure of a conical figure, and much The trunk of the artery which goes out from the right bigger than the heart. It is not fixed to the bafis of the ventricle is called arteria pulmonaris., This trunk, as heart, but round the large veins.above, the aurichsj beit is naturally fituated in the thorax, runs firll of all di- fore they fend off the ramifications, and round the laige rectly upward for a final! fpace, then divides laterally in- arteriesj before their divifions. > to two principal branches, one for each lung; that which The pericardium is made- up of three laminae, the goes to the right lung being the longelt, for a reafon middle and chief of which is compofed of very fine tenthat (hall be given hereafter. dinous filaments, clofely interwoven and crofting, each oThe auricles are mufcular bags fituated at the bafis of ther in different diretticns. The internal lamina feems the heart, one towards the right ventricle, the other to- to be a continuation of the outer coat of the heart, auwards the left, and joined together by an inner feptum, ricleSi and great veffels. The trunks of the aorta and and external communicating fibres, much in the fame pulmonary artery have cne common coat which contains manner with the ventricles; one of them being named the them both as in a fhoath, and is lined on the infide by a right auricle, the other the left. They ar e very uaeveft. cellular fubftacce, chiefly in that fpace which lies between where.
 * he auriculae, and thofe of the fecond lie in the openings The origin or bafis of the pulmonary artery is, in this