THE EPITHELIAL TISSUES. 



65 



or conglomerate gland. There is still another form of gland, in which 

 the ducts begin by a network, as occurs in the liver of man and the 

 higher animals, which may be called a reticular gland. 



The glands are even more vascular than the mucous membranes, of 

 which they may be regarded as extensions. It is especially to be 

 noted that, in no case, is there any direct or open communication be- 

 tween the capillary or other bloodvessels, and the terminal ducts or 

 vesicles of the glands. 



The epithelial and epidermic tissues. These (so named from Greek 

 words which signify that they cover other parts, viz., &re, epi, upon, 

 rtdrj/jLt^ tithemi, I place, and <^/>/-/.a, the skin) are the non-vascular cover- 

 ing tissues which form and, as it were, finish off the actual surfaces of 

 the various secreting membranes and the skin. They all consist of nu- 

 merous agglutinated microscopic particles which are named nucleated 

 cells, because they are more or less vesicular, and always contain a 

 smaller transparent body called a nucleus, which is itself at one time 

 vesicular, and frequently includes one or more still smaller granules 

 called nucleoli (see Figs. 43 and 44). These nucleated cells vary in 

 shape and size ; they are sometimes arranged in one and sometimes in 

 several layers, and cohere together by a minute quantity of interme- 

 diate substance. 



Sometimes, as in the serous membranes, Fig. 43, a (taken from the 



Fig. 43. 



Fig. 43. (Henle and Kolliker.) Various forms of epithelium cells, magnified about 200 diameters, a, 

 polyhedral squamous epithelium from the peritonamm. b, fusiform squamous epithelium from the inte- 

 rior of a vein, c, the same from an artery, d, hexagonal pigment epithelium from the black coat inside 

 the eyeball, e. large squamous epithelium from the mucous membrane of the mouth. /, soft polyhedral 

 glandular epithelium from the liver, or the so-called hepatic cells, g, horny, drj, transparent cells of the 

 epidermis or cuticle. In nearly all the preceding cells, nuclei, nucleoli, and granules are seen. 



peritonaeum), the epithelial cells are flat and polygonal, lying in a 

 single layer, and fitting edge to edge like little scales, or portions of 

 pavement ; hence such an epithelium is called squamous or scaly, tes- 

 sellated or pavemented. Sometimes the cells of the stratified epithe- 

 lium, as in the lip, tongue, and conjunctiva of the eyelids, and also 

 those of the epidermis, are marked with fine lines, or striated; and 

 again the deeper cells are occasionally covered with minute ridges and 

 furrows, or with small spines, so as to be finely denticulate at their 

 borders. In other situations, as in the interior of the veins, b, or 

 arteries, <?, the separate cells are fusiform. In the interior of the eye- 

 ball are certain hexagonal cells, d, which contain much dark coloring 



5 



