The main tissue of tendons (cut longitudinally and transversally) is dense regular connective tissue.

Its intercellular substance is constituted by tightly packaged, thick collagen fiber bundles #1, #2 These bundles are convoluted but run parallel to one another and to the tendon axis (direction of the force vector).
Fibrocytes #1, #2 are found between the fiber bundles, and their elongated nuclei are also parallel to the organ axis.

The transverse section of the tendon shows that nuclei of fibrocytes #1, #2 are rounded, while the cells are stellate, and their band-shaped processes #1, #2 grip the collagen fiber bundles.

The tendon also contains some stripes of loose connective tissue #1, #2 where blood vessels #1, #2 are found.

For more details see Electron microscopy images of intercellular substance of dense regular and dense irregular connective tissues