Textbook of normal histology: including an account of the development of the tissues and of the organs . mplescaly epithelium; those liningthe blood-vessels are elon-gated, irregular spindles, whilethose found in the lymphatic vessels are often still more unsym-metrical, being limited by very tortuous boundaries. For the satisfactory study of endothelium resource to silverstaining (see Appendix) must be had, by which method the inter-cellular cement-substance is colored deeply brown or black, appear-ing as dark, frequently-interrupted boundary-lines. In such prepara-tions the points of union c
Textbook of normal histology: including an account of the development of the tissues and of the organs . mplescaly epithelium; those liningthe blood-vessels are elon-gated, irregular spindles, whilethose found in the lymphatic vessels are often still more unsym-metrical, being limited by very tortuous boundaries. For the satisfactory study of endothelium resource to silverstaining (see Appendix) must be had, by which method the inter-cellular cement-substance is colored deeply brown or black, appear-ing as dark, frequently-interrupted boundary-lines. In such prepara-tions the points of union common to several cells are often markedby small, deeply-stained areas—the stigmata, or figures are regarded by some as minute openings filled bysilver-stained albuminous substances; according to Klein, however,many of these stigmata are the protruding stained processes of con-nective-tissue cells. In addition to these areas of questionable importare true distinct openings, the stomata, which establish direct com-munication with the adjacent lymphatic channels; the diaphragm, 3. mm m Endothelium from peritoneal surface of diaphragm,stained with silver : n, nucleus of endothelial plate ; s,one of the intercellular clefts or stigmata. 34 NORMAL HISTOLOGY. Fig. xo. and especially the septum separating the peritoneal sac from theabdominal lymph-cavity of the frog, exhibit well these pores. The larger stomata are lined byseveral small granular guard-cells, whose expansion andcontraction largely influencethe size of the openings. The development ofepithelium is intimatelyassociated with the exten-sions of the great ecto- andentodermic tracts, since, withthe exception of the epithe-lium of the greater part ofthe genito-urinary organs,the epithelia are the directdescendants of the outer andinner embryonic layers. Thecells lining the passages con-nected with the sexual glands,as well as the urinary tract as far as the bladder, are derived fromthose of the Wolffian
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