Textbook of normal histology: including an account of the development of the tissues and of the organs . one side of the fibre, then extendover the entire periphery, but still forsome time do not reach the centre ofthe fibre, an inner zone of undiffer-entiated sarcoplasm occupying themiddle. Later, this area also becomesconverted into striated tissue, while theonce numerous nuclei are reduced to thefew collected beneath the muscle, likewise, developsfrom the mesoderm immediately surrounding the primary heart-tubes,the contractions of the cells being displayed even before the
Textbook of normal histology: including an account of the development of the tissues and of the organs . one side of the fibre, then extendover the entire periphery, but still forsome time do not reach the centre ofthe fibre, an inner zone of undiffer-entiated sarcoplasm occupying themiddle. Later, this area also becomesconverted into striated tissue, while theonce numerous nuclei are reduced to thefew collected beneath the muscle, likewise, developsfrom the mesoderm immediately surrounding the primary heart-tubes,the contractions of the cells being displayed even before the histo-logical differentiation becomes apparent. In its development itrepresents an intermediate stage, since the original spindle-cells be-come converted into protoplasmic fibres containing a central areawhich always remains less differentiated and nearer its primary con-dition of indifferent sarcoplasm than the peripheral portions of thefibre. The fibres of Purkinje, found in the hearts of certain rumi-nants, represent muscular fibres in which the sarcoplasm remains inpart still Developing voluntary muscle: A,young muscle cells; a, very youngspindle-cell; i, older element, exhibitingindications of future striation on oneside; the remaining part of the cell iscomposed of the undifferentiated sarco-plasm ; B, embryonal muscle-fibres pos-sessing many nuclei and traces of strise;C, developing muscle-fibres in section ;in the larger fibres a differentiatedperipheral zone of striae (d) is seen insection ; an area of still indifferent sar-coplasm occupies the centre of the fibreand surrounds the nucleus («). THE NERVOUS TISSUES. 69 CHAPTER V. THE NERVOUS TISSUES. The nervous system is composed of three principal parts—thetissues originating nervous impulse, the nerve-cells ; the structuresserving to transmit such impulses, the nerve-fibres ; and the tissuesuniting and supporting the nervous elements, the neuroglia andconnective-tissue framework. The nerve-cells
Size: 1331px × 1877px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorpiersolgeorgeageorgea, bookcentury1800, bookdecade1890
