Some muscle fibers end in collagen fibers that continue into the tendon.
The endomysium of other muscle fibers merge with collagen fibers of the tendon.
Tendons may also contain areas of fibrocartilage (#1 and #2) as seen in this specimen.
The collagen fibers in fibrocartilage have an irregular arrangement. While those in the dense regular connective tissue of the tendon have a uniform, parallel arrangement. Fibrocartilage is made by chondrocytes that are round to oval with a clear space surrounding the nuclei. In contrast, the rest of the tendon is made by fibroblasts that are thin, spindle shaped cells tightly applied to the collagen bundles. Both fibrocartilage and dense regular connective tissue contain type I collagen.