Callinectes sapidus (the Blue Crab) is a common crustacean found along the eastern seaboard. The histology of its exoskeleton, as well as the pattern of its molt cycle, have both been well-established by numerous studies. For my Honors project, the inner skeleton of the Blue Crab was examined. Samples were taken from the propodite of the first pereiopod. The tissue sampled has historically been called a tendon since it connects the musculature of the crab to its exoskeleton in all of the appendages. Two tendons were present in the propodite and were referred to as the anterior and posterior tendons due to their positioning while the crab was at rest. The anterior tendon was inserted by the musculus abductor dactylopoditis which moved the dactylopodite outward. The larger posterior tendon was inserted by the musculus adductor dactylopoditis which moved the dactylopodite inward. The study was done by utilizing light miscroscopy in combination with various fixations and staining procedures. The tendon was in fact a new type cuticle, thus was named the inner cuticle. The inner cuticle exhibited unique characteristics not found in outer cuticle, arthrodial membrane, or the inner branchiostegal cuticle. There were two distinct layers: the medial layer and lateral layer. The inner cuticle was found to be an infolding of the external cuticle similar in structure to the inner branchiostegal cuticle of the branchial chamber. Further examination needs to be done to reveal the composition of the junction between the inner cuticle and external cuticle.