The development of the human body; a manual of human embryology . They are formed from the mesenchymeof the dermatomes and from that of the somatic andsplanchnic layers of the mesoderm, but never from themyotomes of the mesodermic somites. The cells from which the heart musculature developsshow at first an irregular protoplasmic reticulum (, A) which later becomes regularly arranged so as to 216 THE DEVELOPMENT OF MUSCLE TISSUE. 217 give the cell when viewed in longitudinal section the ap-pearance of being composed of a series of disks arranged inclosely approximated rows, each disk bein
The development of the human body; a manual of human embryology . They are formed from the mesenchymeof the dermatomes and from that of the somatic andsplanchnic layers of the mesoderm, but never from themyotomes of the mesodermic somites. The cells from which the heart musculature developsshow at first an irregular protoplasmic reticulum (, A) which later becomes regularly arranged so as to 216 THE DEVELOPMENT OF MUSCLE TISSUE. 217 give the cell when viewed in longitudinal section the ap-pearance of being composed of a series of disks arranged inclosely approximated rows, each disk being one of themeshes bounded by the reticulum fibers. Later eachmesh or disk (Fig. 111, B) becomes divided into smallerdisks by reticulum trabeculse which meet in the centers ofthe original disks, and at the lines along which these sec-ondary trabecular meet the reticulum thickens to form afibril (Fig. 111, C, /). The formation of the fibrils beginsat the periphery of the cell and proceeds centrally, thougheven in the adult condition there is an area surrounding. Fig. ill.—Cross-sections of Heart-muscle Cells from Pig Em-bryos OF (A) 10 MM. AND (B AND C) 20 , Fibril; /, large disk; n, nucleus; s, small disk.—(Macallum.) the nucleus in which they do not develop. The cells soaltered arrange themselves at first in bundles distinctlyseparated from one another, so that the heart-wall hasa somewhat spongy appearance, but later the variousbundles fuse more or less completely to form a solid mass,the original condition being retained only in the auricularappendices and on the inner surfaces of the ventricles,where the bundles form the columnar carneae and musculipapillares. The Histogenesis of Striated Muscular Tissue.—The his-togenesis of the striated muscle-fibers resembles very 2l8 THE DEVELOPMENT OF THE HUMAN BODY. closely that described as occurring in the heart muscle,with the difference that the fibrils are developed through-out the entire thickness of the cell, the nucl
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
