Here's some rendered anterior and ventral views of the crazy jaw and toothplates in a young juvenile 🤩 (Lower jaw in red, upper jaw in sky blue)

We end the paper with suggestions for future comparative studies of ICL1 and the function of the OSS. We hope that 3D models like ours will lead to more functional/FEA analyses to understand better the intricacies of fish hearing! 15/15

We also note that, reflective of its anchoring role, rib/vertebra 5 appears like a “transitional vertebra” between the WA and the other thoracic vertebra, bearing in mind that in other species (e.g. catfishes), it is much more heavily modified as part of the WA. 14/

Based on the orientation and composition of ICL1, we argue that it should be included in the category of “Weberian ligaments”, likely functioning to reduce “loose" or "wasted” motion of the OSS and increase the sound sensitivity of the WA. 13/

To my knowledge, this is the first detailed 3D imaging of the triple ligament that tethers together the OSS, tripus, and the anterior face of the swim bladder. 12/

We described the juvenile-adult development of ICL1 along with the other Weberian ligaments, showing they are all mature by 10mm SL. 11/

Histologically, ICL1 closely resembles the interossicular ligament (IOL), with densely packed, taut collagen-1 fibers (unlike the elastin-rich suspensor ligament; SUS), suggesting it strains to hold rib 4/oss in place. 10/

We found that ICL1 bridges features of Weberian and posterior intercostal ligaments, with a unique medial attachment at a steep angle aligned with the os suspensorium (OSS), unlike the slack, flattened posterior ICLs (green). 9/

I wondered if ICL1 could be stabilising the WA but I couldn’t find any mention of this in the literature, so, we reached out to Nathan Bird, an expert on the WA and its histology, and began the super fun collaboration that led to this paper. 8/

Realising it was an intercostal ligament (ICL1), I segmented more posterior ICLs to compare it with, but ICL1 stood out in terms of shape and orientation as it connected the WA to rib 5. 7/

While I was segmenting the area slice by slice, working in axial/sagittal/coronal views, I noticed a small hint of soft tissue running backwards from the fourth rib, and when I segmented it, I saw that it connected rib 4 to rib 5. 6/

The story begins with our 2023 paper using contrast-enhanced synchrotron scanning to describe soft-tissue defects in zebrafish mutants (www.frontiersin.org/journals/end...), in which I spent a lot of time segmenting the Weberian apparatus. 5/

Since being first described more than 200 years ago, the anatomy and diversity of the WA in Otophysi have been well-characterised. We review this prior work in our paper, but our focus is on describing in detail a ligament that is almost entirely absent from the literature. 4/

The swim bladder functions as a resonating chamber, collecting and amplifying sound waves from the environment, transmitting them through the Weberian ossicles and ligaments to the fluid in the ear, leading to the movement of otoliths and stimulation of auditory hair cells. 3/

The Weberian apparatus (WA) refers primarily to the four heavily modified cervical vertebrae of Otophysan fish (10,000 species) that form a chain of small bones and interconnecting ligaments to connect the swim bladder to the inner ear. 2/