AREOLAR TISSUE. 53 



kno\vn as the areolar (including the fat), the fibrous, and the elasfic 

 tissues, and will be now severally treated of. Without disregarding the 

 alliance of cartilage and bone to the connective tissues, we shall not, 

 in imitation of some respected authorities, include them in the same 

 group ; but there remain cercani forms of tissue, occurring locally, or 

 met with as constituents of other textures, which properly belong to 

 this head, and will be briefly considered in a separate section as sub- 

 ordinate varieties of connective tissue. 



CartiLage and bone are included in the group of connective tis^sues or connec- 

 tive substances by several eminent Gennan histologists. and present undoubted 

 points of relationship with these tissues, both in their nature and the general 

 purpose which they serve in the animal frame. Thus, yellow cartilage shows an 

 immistakable transition to elastic connective tissue, as fibro-cartilage does, even 

 more decidedly, to white fibrous tissue. Moreover, the animal basis of bone 

 agrees entirely in chemical composition, and in many points of stmcture, with 

 the last-named tissue. Stm, when it is considered that cartilage, in its tj-pical 

 form, consists of a quite different chemical substance, chondrin. and that bone is 

 characterised by an impregnation of earthy salts, it seems more consistent with 

 the jiiu-pose of histological description to recognise cartilage and bone as inde- 

 pendent tissues. As to their community of oiigin, little stress need be laid on it 

 as a basis of classification, seeing that the origin of blood-vessels, nerves, and 

 muscles, may be traced up to protoplasm-cells, to all appearance similar to those 

 that give rise to the connective tissues, and belonging to the same embryonic 

 layer. 



THE AEEOLAR TISSUE. 



Distribution and arrangement. — If we make a cut through the 

 skin and proceed to raise it from the subjacent parts, we observe 

 that it is loosely connected to them by a soft filamentous substance, 

 of considerable tenacity and elasticit}^ and having, when free fi'om 

 fat, a white fleecy aspect ; this is the substance known by the names 

 of "cellular," " areolar," "filamentous," " connective," and "reticular" 

 tissue ; it used formerly to be commonly called " cellular mem- 

 brane." In like manner the areolar tissue is found underneath the 

 serous and mucous membranes which are spread over various internal 

 surfaces, and serves to attach those membranes to the parts which 

 they line or invest ; and as under the skin it is named " sub- 

 cutaneous," so in the last-mentioned situations it is called " sub- 

 serous " and " submucous " areolar tissue. But on proceeding further 

 we find this substance lying between the muscles, the blood-vessels, and 

 other deep-seated parts, occupying, in short, the intervals between the 

 different organs of the body where they are not otherwise insulated, and 

 thence named " intermediate ; " very generally, also, it becomes more 

 consistent and membranous immediately around these organs, and, 

 under the name of the " investing " areolar tissue, affords each of them 

 a special sheath. It thus forms inclosing sheaths for the muscles, the 

 nerves, the blood-vessels, and other parts. Whilst the areolar tissue 

 might thus be said in some sense both to connect and to insulate entire 

 organs, it also performs the same oflfice in regard to the finer parts of 

 which these organs are made up ; for this end it enters between the 

 fibres of the muscles, uniting them into bundles ; it connects the several 

 membranous layers of the hollow viscera, and binds together the lobes 

 and lobules of many compound glands ; it also accompanies the vessels 

 and nerves within these organs, following their branches nearly to their 

 finest divisions, and affording them support and protection. This portion 



