/usr/include/Inventor/C/ is in libcoin80-dev 3.1.4~abc9f50+dfsg3-2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/Inventor/C/XML/
/usr/include/Inventor/C/XML/attribute.h
/usr/include/Inventor/C/XML/document.h
/usr/include/Inventor/C/XML/element.h
/usr/include/Inventor/C/XML/entity.h
/usr/include/Inventor/C/XML/parser.h
/usr/include/Inventor/C/XML/path.h
/usr/include/Inventor/C/XML/types.h
/usr/include/Inventor/C/XML/world.h
/usr/include/Inventor/C/base/
/usr/include/Inventor/C/base/hash.h
/usr/include/Inventor/C/base/heap.h
/usr/include/Inventor/C/base/list.h
/usr/include/Inventor/C/base/math-undefs.h
/usr/include/Inventor/C/base/memalloc.h
/usr/include/Inventor/C/base/rbptree.h
/usr/include/Inventor/C/base/string.h
/usr/include/Inventor/C/base/time.h
/usr/include/Inventor/C/basic.h
/usr/include/Inventor/C/errors/
/usr/include/Inventor/C/errors/debugerror.h
/usr/include/Inventor/C/errors/error.h
/usr/include/Inventor/C/glue/
/usr/include/Inventor/C/glue/dl.h
/usr/include/Inventor/C/glue/gl.h
/usr/include/Inventor/C/glue/spidermonkey.h
/usr/include/Inventor/C/threads/
/usr/include/Inventor/C/threads/barrier.h
/usr/include/Inventor/C/threads/common.h
/usr/include/Inventor/C/threads/condvar.h
/usr/include/Inventor/C/threads/fifo.h
/usr/include/Inventor/C/threads/mutex.h
/usr/include/Inventor/C/threads/recmutex.h
/usr/include/Inventor/C/threads/rwmutex.h
/usr/include/Inventor/C/threads/sched.h
/usr/include/Inventor/C/threads/storage.h
/usr/include/Inventor/C/threads/sync.h
/usr/include/Inventor/C/threads/thread.h
/usr/include/Inventor/C/threads/worker.h
/usr/include/Inventor/C/threads/wpool.h
/usr/include/Inventor/C/tidbits.h