Morphology of the Bearded Seal (Erignathus barbatus) Muscular-Vibrissal Complex: A Functional Model for Phocid Subambient Pressure Generation.
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Bearded seals possess a broad muscular snout with large mystacial vibrissal fields that are involved in tactile sensation and prey identification. Although the microstructure of bearded seal vibrissae and their feeding performance have been investigated their orofacial morphology has not. Such morphological studies are important to understand the underlying mechanisms of feeding performance and to test proposed functional hypotheses. Therefore, the facial musculature was examined in bearded seals to test functional hypotheses regarding feeding performance. The orofacial musculature is composed primarily of three enlarged muscular layers, the M. levator nasolabialis, M. orbicularis oris, and M. buccinatorius (superficial), M. maxillonasolabialis (intermediate), and the M. lateralis nasi and M. dilator nasi (deep). The expansion of these muscles, the three dimensionality of the entire muscular array, the soft tissue insertions, and constant volume fit the model of a muscular hydrostat, and explains the detailed and varied mobility of their snout. An anastomosing network of CN VII innervates these facial muscles. The disproportionately large infraorbital nerve of CN V courses toward the snout and divides into numerous branches that penetrate the external capsule of every Follicle Sinus-Complex. The anatomical evidence support that the M. orbicularis oris, M. buccinatorius, and M. maxillonasolabialis form a robust lateral lip complex that can occluded lateral gape during subambient pressure generation. The rostral portion of the M. orbicularis oris, M. dilator nasi, and M. mentalis function to pursue the rostral lips to form a circular aperture important for projecting steep pressure gradients rostral to the lips for prey acquisition. Anat Rec, 299:1043-1053, 2016. 2016 Wiley Periodicals, Inc.
