Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/904

Rh 850 jconnect together the two structures between which the tendon or ligament passes. In the fibrous form of connective tissue, both cells and intercellular substance, the latter of which is differentiated into fibres, may be recognised. The cells are, as a rule, either elongated, or fusiform, or caudate, or stellate branched cells, and are familiarly known as the connective tissue corpuscles. In these cells the nucleus is round or oval, and usually well marked. It is surrounded by granular proto plasm, but it is very doubtful if the protoplasm is invested by a cell wall. Not unf requently, more especially where the cells are stellate, the delicate branched protoplasm processes of adjacent cells appear to blend at their extremities with each other, and form an anastomosing network. In tend ons the cells are arranged in linear rows, which lie parallel to the long axis of the tendon itself. In adults these cells are flattened, but in younger tendons they are more poly gonal in form. There seems reason to think, indeed, as Thin has shown, that the bundles of connective tissue are invested by a layer of flattened cells. The wide dif fusion of the connective tissue throughout the body, and the great importance of its cellular elements, have been especially dwelt on by Virchow as sources of origin of the new cell forms which arise in various pathological processes. The intercellular substance consists of fibres, which are not uniform in shape, and are divided into the two groups of white and yellow fibres. The white .fibres of connective tissue constitute the most common form, and make up the great bulk of most ligaments, tendons, and fibrous membranes. They consist of excessively delicate filaments, varying from ^^th to T7 ^ T th inch in thickness, which are united together in bundles or fasciculi of variable size. The bundles, as well as the filaments of which they are composed, have a wavy course, and the filaments in each bundle lie almost parallel to each other. The bundles also v , in some cases are parallel, though in others M they cross at various angles. Not only the filaments in each bundle, but the bundles themselves, are cemented together ; the firm ness of the adhesion varies in the different FIG. 39.Fasdcuii modifications of the fibrous connective tissue, f * connective being much more decided in the tendons, tissue - ligaments, and fasciae, than in the lax areolar tissue. The yellow fibres of connective tissue, named elastic fibres, from their elasticity, make up the mass of the liga- .mentum nuchse, the ligainenta sub-flava, and the yellow .elastic coat of the arteries. They are also found, mingled with the white fibres, in the fibrous membranes, the skin, mucous and serous membranes, the areolar tissue, in ten dons, and some ligaments. In the liga- menta sub-flava and nuchse the yellow fibres are arranged in bundles, the in dividual fibres of which are comparatively broad, with a distinct dark outline. They branch, and their branches readily break across, and the broken end then curls upon itself. Their diameter is about rcVifth i ncn - In the coats of the arteries the elastic fibres form an anastomosing network. When mingled with the white fibres they are much finer, and sometimes do not exceed 5T ^ 7 th inch in diameter. They possess, however, a distinct and do- finite outline; they branch and occasion- ally anastomose; and the individual fibres, possessing a ring- like, spiral, or twisted course, are wound around the bundles of the white fibres. The white fibres yield gelatine on boil- clastic tissue from u e amcntum nuchK - [ANATOMY OF ing, but the elastic fibres do not. The white fibres swell up and become so transparent under the action of acetic acid as to be no longer recognisable. The yellow fibres, again are not affected by that reagent. Quekett pointed out that the elastic fibres of the ligamentum nuchee of the giraffe were marked by transverse striee, and M. Watson has seen a similar appearance in the elastic pericardiac ligament of the elephant. These transverse strite are apparently cracks in the fibre; and, as Beale has shown, are not unf requently seen in the elastic fibres in beef and mutton which have passed through the alimentary canal. Bearing on the mode of nutrition of the tendons, and other fibrous forms of connective tissues, the existence of plasma, or juice, canals has been described, along which, not blood, but the liquor sanguinis is supposed to flow. Yirchow conceived that the connective tissue corpuscles formed an anastomosing network for this purpose. Briicke believed that delicate channels or lacunas existed between the bundles of connective tissue, whilst Eecklinghausen maintained that serous canaliculi were situated in the homogeneous substance which connects the fibrous fasciculi and larnellas of the connective tissue with each other. These lacuna} or caualiculi are, in all probability, the root lets of origin of the lymphatic system of vessels. There can indeed be no doubt, as the recent injections of Ludwig and Schweigger-Seidel have shown, that tendons and fasciae are well provided with lymph vessels, for they have in jected in them a minute net work, consisting in part of polygonal meshes, and in part of vessels running longitudin ally and parallel to the con nective tissue bundles, and the walls of these vessels were formed of endothelial cells. Recklinghausen and others have recently described cor puscles in the connective tissue which resemble in size and appearance the white cor puscles of the blood and lymph. These corpuscles are believed to move about in the juice canals already referred to, and it is possible that they may have migrated into the tissue through the walls of its nutrient blood-vessels. The vascularity of the connective tissue varies in differ ent localities. The periosteum and perichondrium are very vascular; but their numerous vessels are concerned in the nutrition not merely of these fibrous membranes, but of the bone and cartilage which they invest. The sheath of connective tissue which invests a tendon is more vascular than the substance of the tendon itself. As a rule, it may be stated that the fibrous connective tissues are not highly vascular, and that the nutritive changes which take place in them after their growth is completed are not very active. The mode of development of the connective tissue has Bevel i been much discussed by anatomists, and various views have ment been advanced as to the changes which lead to its pro- JJJJJJ* duction. It is now, however, generally admitted that it arises from the embryonic cells by a special morphological and chemical differentiation of their protoplasm, but the degree to which this differentiation may proceed varies with the particular form of the textiire. In the neuroglia the, tissue is apparently a simple nucleated protoplasm. In the retiform connective tissue the cells have assumed a stellate shape, and their branches anastomose. In the gelatinous and fibrous forms an intercellular matrix is extensively pro- duced, and exhibits a differentiation into fibres. In these last-named forms, which are the most characteristic varie- ties of the tissue, the cells of the embryo change their form, 10. 41. Connective tissue of the omentum of the fcctus, showing !l:u characteristic fusiform corpuscles. A capillary blood-vessel crosses ti.e figure, and near it are several blooit corpuscles which have probally migrated from the vessel.