“…It has been hypothesized that this arrangement of long, straight-chain FA surrounding an inner core of shorter and branched FA and WE serves to focus the outgoing echolocation beams from the melon and the incoming sounds through the MFBs to the ear, because sound travels more slowly through the WE and shorter, branched FA than through TAG and the longer, straight chain FA (Koopman et al, 2006;Litchfield et al, 1973;Varanasi et al, 1975). While this hypothesis has been supported by measurements of sound through different regions of the melon (Goold & Clarke, 2000;Yamato et al, 2014), other studies have concluded that a large portion of sound refraction and collimation happens at the interface between the water and outer melon tissue rather than within the acoustic fat (Litchfield & Greenberg, 1979), and very little is known about how sound is received by the jaw fats and subsequently transferred to the ears. It is generally assumed that sound enters the fat bodies lying superficial to the mandible (the extra-mandibular fat bodies or EMFB), and then transferred across the thin portion of the mandible (the "pan bone," known as Norris' acoustic window) to the fat bodies lying within the mandibular fossa (the intramandibular fats bodies or IMFB) for conduction to the ear bones, which have a direct connection to the posterior portion of the IMFB (Koopman et al, 2006;Norris, 1968).…”