The development of the human body; a manual of human embryology . ver; W, Wolffian body.—(Toldt and Zuckerkandl.) blood-vessels, and so divided into numerous anastomosingtrabecular (Fig. 175). These are at first irregular in sizeand shape, but later they become more slender and moreregularly cylindrical, forming what have been termed thehepatic cylinders. In the center of each cylinder, wherethe cells which form it meet together, a fine canal appears,the beginning of a bile capillary, the cylinders thus be-coming converted into tubes with fine lumina. This oc- 328 THE DEVELOPMENT OF THE HUMAN
The development of the human body; a manual of human embryology . ver; W, Wolffian body.—(Toldt and Zuckerkandl.) blood-vessels, and so divided into numerous anastomosingtrabecular (Fig. 175). These are at first irregular in sizeand shape, but later they become more slender and moreregularly cylindrical, forming what have been termed thehepatic cylinders. In the center of each cylinder, wherethe cells which form it meet together, a fine canal appears,the beginning of a bile capillary, the cylinders thus be-coming converted into tubes with fine lumina. This oc- 328 THE DEVELOPMENT OF THE HUMAN BODY. curs at about the fourth week of development and at thistime a cross-section of a cylinder shows it to be composedof about three or four hepatic cells (Fig. 176, A), amongwhich are to be seen groups of smaller cells (e) which areerythrocytes, the liver having assumed by this time itshaematopoietic function (see p. 244). This condition ofaffairs persists until birth, but later the cylinders undergoan elongation, the cells of which they are composed slip-. Fig. 176.—Transverse Sections of Portions op the Liver op (A) a Fetus of Six Months and (B) a Child op Four , Bile capillary; e, erythrocyte; he, hepatic cylinder.—(Toldt and Zuckerkandl.) ping over one another apparently, so that the cylindersbecome thinner as well as longer and show for the mostpart only two cells in a transverse section (Fig. 176, B);and in still later periods the two cells, instead of lyingopposite one another, may alternate, so that the cylindersbecome even more slender. The bile capillaries seem to make their appearance firstin cylinders which lie in close relation to branches of the THE LIVER. 329 portal vein (Fig. 177) and thence extend throughout theneighboring cylinders, anastomosing with capillaries de-veloping in relation to neighboring portal branches. Asthe extension so proceeds the older capillaries continue toenlarge and later become transformed into bile-ducts (, C),
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
