Henry Gray (1825–1861). Anatomy of the Human Body. 1918.
3. Tendons, Aponeuroses, and Fasciæ
Tendons are white, glistening, fibrous cords, varying in length and thickness, sometimes round, sometimes flattened, and devoid of elasticity. They consist almost entirely of white fibrous tissue, the fibrils of which have an undulating course parallel with each other and are firmly united together. When boiled in water tendon is almost completely converted into gelatin, the white fibers being composed of the albuminoid collagen, which is often regarded as the anhydride of gelatin. They are very sparingly supplied with bloodvessels, the smaller tendons presenting in their interior no trace of them. Nerves supplying tendons have special modifications of their terminal fibers, named organs of Golgi. 1 Aponeuroses are flattened or ribbon-shaped tendons, of a pearly white color, iridescent, glistening, and similar in structure to the tendons. They are only sparingly supplied with bloodvessels. 2 The tendons and aponeuroses are connected, on the one hand, with the muscles, and, on the other hand, with the movable structures, as the bones, cartilages ligaments, and fibrous membranes (for instance, the sclera). Where the muscular fibers are in a direct line with those of the tendon or aponeurosis, the two are directly continuous. But where the muscular fibers join the tendon or aponeurosis at an oblique angle, they end, according to Kölliker, in rounded extremities which are received into corresponding depressions on the surface of the latter, the connective tissue between the muscular fibers being continuous with that of the tendon. The latter mode of attachment occurs in all the penniform and bipenniform muscles, and in those muscles the tendons of which commence in a membranous form, as the Gastrocnemius and Soleus. 3 The fasciæ are fibroareolar or aponeurotic laminæ, of variable thickness and strength, found in all regions of the body, investing the softer and more delicate organs. During the process of development many of the cells of the mesoderm are differentiated into bones, muscles, vessels, etc.; the cells of the mesoderm which are not so utilized form an investment for these structures and are differentiated into the true skin and the fasciæ of the body. They have been subdivided, from the situations in which they occur, into superficial and deep. 4 The superficial fascia is found immediately beneath the integument over almost the entire surface of the body. It connects the skin with the deep fascia, and consists of fibroareolar tissue, containing in its meshes pellicles of fat in varying quantity. Fibro-areolar tissue is composed of white fibers and yellow elastic fibers intercrossing in all directions, and united together by a homogeneous cement or ground substance, the matrix. 5 The cells of areolar tissue are of four principal kinds: (1) Flattened lamellar cells, which may be either branched or unbranched. The branched lamellar cells are composed of clear cytoplasm, and contain oval nuclei; the processes of these cells may unite so as to form an open network, as in the cornea. The unbranched cells are joined edge to edge like the cells of an epithelium; the “tendon cells,” presently to be described, are examples of this variety. (2) Clasmatocytes, large irregular cells characterized by the presence of granules or vacuoles in their protoplasm, and containing oval nuclei. (3) Granule cells (Mastzellen), which are ovoid or spheroidal in shape. They are formed of a soft protoplasm, containing granules which are basophil in character. (4) Plasma cells of Waldeyer, usually spheroidal and distinguished by containing a vacuolated protoplasm. The vacuoles are filled with fluid, and the protoplasm between the spaces is clear, with occasionally a few scattered basophil granules. 6