. A text-book of human physiology . er into the papillary mus-cles and chordte tcndineae, orinto the atrio-ventricular two layers thus formed are separated by a median layer, which, when isolated by a special methodof preparation, has the form of a muscular cone. It is connected also by manyfibers with the outer and inner layers. The fibers of this median part describeloops, which, not having any tendinous connections, return to their starting point(Fig. 52). It is obvious that this strongly developed median layer must play a prominent part in the contrac-tion of the left ventricle. T
. A text-book of human physiology . er into the papillary mus-cles and chordte tcndineae, orinto the atrio-ventricular two layers thus formed are separated by a median layer, which, when isolated by a special methodof preparation, has the form of a muscular cone. It is connected also by manyfibers with the outer and inner layers. The fibers of this median part describeloops, which, not having any tendinous connections, return to their starting point(Fig. 52). It is obvious that this strongly developed median layer must play a prominent part in the contrac-tion of the left ventricle. The synchronism of con-traction of the two ventriclesnaturally depends on the factthat the muscular fibers arein part common to both ven-tricles. Xevertheless variousobservations indicate that thissynchronism is not an absoluteone, but that each ventriclepossesses a certain pJii/siolog-icat independence (Knoll). Fig. 51.—Cross-section through a fully contractedhuman heart at the junction of the upper andmiddle thirds, after B. THE FORM CHANGES OFTHE HEART FiG. 52.—Layer of fibers in the left ventricle of thehuman heart which have no tendinous more external and more internal layers havebeen removed. The outline of the entire heart isshown. After Krehl. In diastole the form of theventricles of an empty heartoutside the body depends in themain upon the way in whichthey are supported, whereas 164 CIRCULATION OF THE BLOOD iindor normal circumstances their form depends in the main upon the degreeto which they are filled. In systole when, as Harvey put it, the heart makestense all of its fibers, the ventricles whether empty or filled have a perfectlydefinite form, which is entirely independent of the diastolic form. Hence ifthe heart is lengthened in any one of its diameters during diastole, it is short-ened in this diameter during systole. In the living body and in the unopened chest the heart lies in the peri-cardium and is covered for the most part by the
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectphysiology, bookyear1
