. Anatomischer Anzeiger. Anatomy, Comparative; Anatomy, Comparative. 615 At the periphery of the cell the fibril bundles are surrounded in the same way by small sarcoplasmic discs, so that their outer limits make up the boundaries of the cell, forming a sort of cell membrane. The sarcoplasm surrounding the nucleus at the centre of the cell, where fibril bundles are absent, is made up of similar discs, but here they are somewhat larger than at the periphery. The main features to be observed in a cross section then are the following: 1) The presence of fibril bundles usually in the form of leaf-
. Anatomischer Anzeiger. Anatomy, Comparative; Anatomy, Comparative. 615 At the periphery of the cell the fibril bundles are surrounded in the same way by small sarcoplasmic discs, so that their outer limits make up the boundaries of the cell, forming a sort of cell membrane. The sarcoplasm surrounding the nucleus at the centre of the cell, where fibril bundles are absent, is made up of similar discs, but here they are somewhat larger than at the periphery. The main features to be observed in a cross section then are the following: 1) The presence of fibril bundles usually in the form of leaf-like bands, arranged radially around the periphery of the cell, internal to which are smaller polygonal masses, situated irregularly between the peripheral radially disposed masses and the central perinuclear sarco- plasm. 2) The breaking up of the sarcoplasm into regular small discs which surround the fibril bundles. The membranes of those small discs which reach the surface of the cell go to make up the external limits of the latter. It is to be emphasized -. then, that in the protoplasm of the adult heart muscle cell, there are columns of fibrils which run longitudinally sur- /S*I^^^^^y1'vSx2B-^ Q. rounded by sarcoplasm, in the way that each bundle is sur- rounded by a varying number of small sarcoplasmic discs, the horizontal separating partitions of which are continuous with Krause's line on the fibril bun- dles. This may be schema- tically represented as in Fig. Fig. 5. Diagram of the structure of adult human heart muscle. F fibril bundle; S small sarcoplasmic disc; Q Querscheibe. Heart Muscle of other Animals. The muscle found in hearts from other animals is essentially the same in structure as that described above, differing only in the mode of union of the cells. The heart tissue of the pig, dog, cat, rabbit and mouse was examined, and the structure in every case was found to be practically identical with that described for human heart muscle. In the heart of the s
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