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The melon is a lipid-rich structure located in the forehead of odontocetes that functions to propagate echolocation sounds into the surrounding aquatic environment. To date, the melon's ability to guide and impedance match biosonar sounds to seawater has been attributed to its unique fatty acid composition. However, the melon is also acted upon by complex facial muscles derived from the m. maxillonasolabialis. The goal of this study was to investigate the gross morphology of the melon in bottlenose dolphins (Tursiops truncatus) and to describe how it is tendinously connected to these facial muscles. Standard gross dissection (N = 8 specimens) and serial sectioning (N = 3 specimens) techniques were used to describe the melon and to identify its connections to the surrounding muscles and blubber in three orthogonal body planes. The dolphin forehead was also thin-sectioned in three body planes (N = 3 specimens), and polarized light was used to reveal the birefringent collagen fibers within and surrounding the melon. This study identified distinct regions of the melon that vary in shape and display locally specific muscle-tendon morphologies. These regions include the bilaterally symmetric main body and cone and the asymmetric right and left caudal melon. This study is the first to identify that each caudal melon terminates in a lipid cup that envelopes the echolocation sound generators. Facial muscles of the melon have highly organized tendon populations that traverse the melon and insert into either the surrounding blubber, the connective tissue matrix of the nasal plug, or the connective tissue sheath surrounding the sound generators. The facial muscles and tendons also lie within multiple orthogonal body planes, which suggest that the melon is capable of complex shape change. The results of this study suggest that these muscles could function to change the frequency, beam width, and directionality of the emitted sound beam in bottlenose dolphins. The echolocation sound propagation pathway within the dolphin forehead appears to be a tunable system., (Copyright 2008 Wiley-Liss, Inc.)

In this study the pattern of arthrodial membrane deposition in Callinectes sapidus was determined by histological and ultrastructural examination of tissues from the carpus joint of the cheliped collected during premolt, ecdysis, postmolt, and intermolt. Apolysis in the arthrodial membrane occurs at stage D(0) and is synchronous with apolysis of the calcified cuticle. Epicuticle formation begins at early stage D(1) and is completed in late stage D(1). Procuticle deposition starts at D(2) and continues until ecdysis. Numerous cytoplasmic extensions occur throughout the lamellae. Component fibers of the arthrodial membrane are intimately associated with dense plaques on the apical membrane of the underlying hypodermal cells, suggesting a site for fiber polymerization. Deposition of the arthrodial membrane continues after ecdysis, with most of the cuticle thickening occurring during stage C. When stained with PAS and counterstained with hematoxylin, a difference can be discerned between preecdysial and postecdysial procuticle of the arthrodial membrane, a distinction not made in previous studies. The boundary between the arthrodial membrane and calcified cuticle is thicker than either of the two layers and the layers overlap rather than butting up against one another. This pattern suggests that underlying hypodermal cells have to produce multiple types of cuticle over the molt cycle. A summary of the various molting patterns in C. sapidus suggests that the control of these diverse events may prove to be complex., (Copyright 2003 Wiley-Liss, Inc.)