THE CONNECTIVE TISSUE. 43 



glands, as we shall hereafter see, are but appendages or extensions of the 

 mucous membrane, which is prolonged into their ducts. The mucous mem- 

 brane of the tongue is formed of a layer of condensed areolar connective tissue 

 covered by an epithelium. Its epithelium is of the kind called squamous. The 

 epithelium covering the mucous membrane of the interior of the larynx and 

 windpipe is columnar and ciliated, i.e., provided with microscopic lash-like 

 moving organs called cilia. 



The tissues thus enumerated and demonstrated from the sheep's tongue and 

 larynx may even be used for microscopical examination to illustrate the descrip- 

 tions now to be given of the human tissues. A few special tissues, such as the 

 brain substance, the substance of peculiar glands, and the parts of the organs 

 of the senses, as well as pure articular cartilage, and white nbro-cartilage, may 

 be taken also from the sheep. There is, however, no skin like the human skin. 



In examining the tissues microscopically a common watchmaker's lens may 

 be first employed upon them. Afterwards those tissues which are composed 

 of filamentous or tubular elements may be prepared for the compound micro- 

 scope by pulling or tearing asunder by means of needles, the constituent parts 

 of a small portion, the size of a pin's head, placed in a drop or two of water 

 on a piece of glass. Of the solid tissues a very thin section must be made, and 

 put on glass in a drop of water. Thus prepared the specimens must be cov- 

 ered with the fine glass seld for that purpose, and then they may be examined 

 under the compound microscope as transparent objects. The epithelial cov- 

 erings of membranes merely require to be scraped off and moistened with a 

 drop of water. Various reagents are employed to alter the tissues under ex- 

 amination, as will be mentioned hereafter. The order in which the several 

 tissues will now be described is one of convenience only. The mode in which 

 they may be classified will be stated in the physiological section of the work. 



THE MICROSCOPIC STRUCTURE OF THE TISSUES OF THE HUMAN BODY. 



Connective tissue. This tissue exists in two forms, areolar and 

 fibrous. The areolar form connects organs and parts of organs to- 

 gether, supports their vessels and nerves, and allows of a certain move- 

 ment amongst them ; it consists of a loose moist extensible web, com- 

 posed of interlacing bundles and bands, having intervals between them 

 called areolce or cells, whence it is named also cellular tissue. These 

 areolse communicate through the whole body, and are the spaces in 

 which the fat is lodged, and in which fluid collects in general dropsy. 

 Under the skin, and the mucous and other membranes, the areolar 

 connective tissue is named subcutaneous, submucous, and so on. In a 

 more condensed form it constitutes the basis of those membranes them- 

 selves. 



The bundles of this tissue are made up of delicate transparent 

 colorless filaments, Fig. 17, a, held together by moist homogeneous 

 matter. The filaments are wavy, and do not branch ; and the bun- 

 dles interlace in all directions : hence the flexibility and extensibility 

 of this widely spread and important tissue. Its resiliency is due to 

 the intermixture of numerous exceedingly fine fibres of elastic tissue. 



The fibrous form of the connective tissue consists of the same ele- 

 ments as the areolar form, viz., colorless filaments mixed with fine 

 elastic fibres ; but the white filaments, instead of being in open inter- 

 laced bundles, are arranged in close parallel ones, having a shining 

 aspect, and marked with faint cross waves. Fig. 17, b. The fibrous 

 tissues, therefore, are not loose and extensible, but strong, unyielding 

 and glistening. Straight intersecting bands, held firmly together in 



