Vascularization of a lobster muscle

The vascularization of the distal accessory flexor muscle (DAFM) in the walking legs of the lobster, Homarus americanus, was examined with dye injection and electron microscopy. Vascularization of this flat, thin DAFM is via two vessels, one supplying the tendinal region of the muscle and the other the exoskeletal region. The vessels that originate from the single major limb vessel, subdivide extensively over the DAFM and form a profuse network that has hitherto gone unnoticed. The degree of vascularization of individual fibers was determined by periodic sampling along its length with thin-section electron microscopy. At each and every sampling station, individual fibers had several (seven to eight), small-diameter (4 μm) blood vessels in their cross-sectional profile. In contrast, nerve terminals of the excitor and inhibitor axon were rarely encountered. This high degree of vascularization was found amongst fibers that are from different regions of the DAFM and differ in the performance of their excitatory synapse but are similar in their structural and contractile properties.