Linings are strips of wood glued to the top and bottom of the sides to add rigidity to the sides, and maybe more importantly, to add glue are when the front and the back are glued to the sides. The linings are typically morticed to the corner blocks. With the last cello I had a lot of trouble with the linings. They kept breaking. This time I bought wood actually meant for the linings. I hope things will go smoother this time. Anyways, I started the work by cutting the mortices into the corner blocks for one of the c bout linings. The practice here also differs. Some cut a rectangular mortice, Strobel saws them at 45° and so will I. Seems easier than trying to chisel them out fully.

Here are some links to other resources:
Youtube: Lucas Fabro MAKING A CELLO | Preparing and gluing the Lining
guitars.davidalabaster.com/cello-week-3-the-ribs/
​osnesviolins.com/5.Bending%20the%20ribs.htm

I came across a video where Davide Sora talks about his approach to violin making. I really like his videos on his YouTube channel. Nice to hear and see the person behind the craft.

​I found some nice photos from a cello build at www.geigenmacher.at/fachliches/exkurs-cellobau/.