COLLAGENOUS AND ELASTIC CONNECTIVE TISSUES 'u 



of the wall of thr <i;ut in all vcrtchratcs, and portions of the wall of 

 large })loo(l\'essels. Its distrihntion and occnrrence \ary in dilferent 

 animals. 



The regnlarly arranged dense tissue usually has either eollagenous 

 or elastic fibers predominating. In the corneum of the eye a dense 

 collagenous tissue is present. The dermis of some animals, as 

 exemplified by the frog, has a tissue of similar collagenous composi- 

 tion. A whole group of structures having a regular arrangement 

 of the tissue elements are classified as tendons and ligaments. 



Tendons.— Tendons are composed of closely packed bundles of 

 collagenous fibrils arranged })aralleling each other to form cords 

 connecting muscles to bones. The fibrils are held together with a 

 cementing grt)und substance and the entire tendon is surrounded 

 by a sheath of loosely and irregularly arranged fibroelastic connec- 

 tive tissue which extends into the tendon to ensheath bundles of 

 fibrils. A characteristic feature of tendons is the location of 

 the cells, which are mainly fibrocytes. These cells cannot 

 be wholly identified in sectioned preparations, but their nuclei 

 appear as deeply stained elongated oval structures. They are 

 located near each other in the region between adjacent bundles of 

 fibrils. The cell form is modified by the compression of the closely 

 packed fibrils; the cytoplasm extends out between the adjacent 

 bundles so that each cell appears to have several flat wings. In 

 longitudinal sections the fibrillar composition of the bundles is 

 indicated by faint longitudinal striations. These structures supply 

 a tough but inelastic connection primarily between the bones and 

 muscles. 



Ligaments.— Ligaments are tough fibrous bands which structurally 

 resemble tendons except that they may be less regularly arranged 

 and contain elastic fibers in considerable quantity. Ligaments 

 commonly connect two bones where they form a joint. One in 

 particular, the ligamentum michse, prominent in large quadrui^eds, 

 such as cattle, is especially rich in elastic fibers. It forms a strong 

 elastic support connecting the skull with the spinous processes of 

 the cervical and thoracic vertebrtie. It is composed of bundles of 

 elastic fibers paralleling each other and harnessed together with 

 loosely organized fibroelastic connective tissue. Such a structure 

 does not fatigue easily when stretched, and is admirably suited to 

 the demands of grazing animals. 



Not all ligaments connect bone with bone. In other loca- 



