Morphology of the melon and its tendinous connections to the facial muscles in bottlenose dolphins (Tursiops truncatus)

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Cally Harper (Creator)
Institution
The University of North Carolina Wilmington (UNCW )
Web Site: http://library.uncw.edu/
Advisor
Ann Pabst

Abstract: The melon is a lipid rich structure located in the odontocete forehead that functions to propagate echolocation sounds into the surrounding aquatic environment. To date, the melon’s abilities to guide and impedance match biosonar sounds to water has been attributed to its unique fatty acid composition. The melon, though, is also acted upon by facial muscles (rostral, pars anterointernus, and nasal plug muscles). The goals of this study were to investigate the gross morphology of the melon in the bottlenose dolphin (Tursiops truncatus) and to describe how it is tendinously connected to these facial muscles. Standard gross dissection (n = 8) and serial sectioning (n = 3) techniques were used to describe the melon and to identify the connections between it and the surrounding muscles and blubber in three orthogonal body planes. The melon was also thin-sectioned in three body planes (n = 3) and polarized light was used to reveal the birefringent collagen fibers within and surrounding the melon. This study identified two distinct regions of the melon, the main body and the caudal melon. The caudal melon is bilaterally asymmetrical. This study is the first to identify three regions of the right caudal melon, termed the cup, stem, and cone and two regions of the left caudal melon, named the cup and branch. All regions of the melon vary in shape and display locally specific muscle-tendon morphologies. The entire length of the melon, from the initial site of sound generation to its rostral end, is acted upon by facial muscles. These muscles 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 planes, which suggest that the melon is capable of changing its shape in multiple planes. Thus, the sound propagation pathway from the echolocation sound generators to the surrounding water appears to be a tunable system. Specifically, the facial muscles are hypothesized to be able to change the frequency, beam width, and directionality of the emitted sound beam in bottlenose dolphins (Tursiops truncatus).

Additional Information

Publication
Thesis
A Thesis Submitted to the University of North Carolina at Wilmington in Partial Fulfillment of the Requirement for the Degree of Masters of Science
Language: English
Date: 2009
Keywords
Bottlenose dolphin--Morphology, Bottlenose dolphin--Physiology, Bottlenose dolphin--Sense organ, Cetacea--Morphology, Echolocation (Physiology)
Subjects
Echolocation (Physiology)
Bottlenose dolphin -- Morphology
Bottlenose dolphin -- Physiology
Cetacea -- Morphology
Bottlenose dolphin -- Sense organ