/usr/include/ptlib/msos/ is in libpt-1.10.10-dev 1.10.10-3.1ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/ptlib/msos/AUTOEXP.DAT
/usr/include/ptlib/msos/ptlib/
/usr/include/ptlib/msos/ptlib.dtf
/usr/include/ptlib/msos/ptlib.ignore
/usr/include/ptlib/msos/ptlib/channel.h
/usr/include/ptlib/msos/ptlib/conchan.h
/usr/include/ptlib/msos/ptlib/config.h
/usr/include/ptlib/msos/ptlib/contain.h
/usr/include/ptlib/msos/ptlib/critsec.h
/usr/include/ptlib/msos/ptlib/debstrm.h
/usr/include/ptlib/msos/ptlib/dynalink.h
/usr/include/ptlib/msos/ptlib/epacket.h
/usr/include/ptlib/msos/ptlib/ethsock.h
/usr/include/ptlib/msos/ptlib/file.h
/usr/include/ptlib/msos/ptlib/filepath.h
/usr/include/ptlib/msos/ptlib/icmpsock.h
/usr/include/ptlib/msos/ptlib/ipdsock.h
/usr/include/ptlib/msos/ptlib/ipsock.h
/usr/include/ptlib/msos/ptlib/ipxsock.h
/usr/include/ptlib/msos/ptlib/mail.h
/usr/include/ptlib/msos/ptlib/mutex.h
/usr/include/ptlib/msos/ptlib/pdirect.h
/usr/include/ptlib/msos/ptlib/pipechan.h
/usr/include/ptlib/msos/ptlib/pprocess.h
/usr/include/ptlib/msos/ptlib/ptime.h
/usr/include/ptlib/msos/ptlib/ptlib.inl
/usr/include/ptlib/msos/ptlib/remconn.h
/usr/include/ptlib/msos/ptlib/semaphor.h
/usr/include/ptlib/msos/ptlib/serchan.h
/usr/include/ptlib/msos/ptlib/sfile.h
/usr/include/ptlib/msos/ptlib/socket.h
/usr/include/ptlib/msos/ptlib/sound.h
/usr/include/ptlib/msos/ptlib/sound_directsound.h
/usr/include/ptlib/msos/ptlib/sound_win32.h
/usr/include/ptlib/msos/ptlib/spxsock.h
/usr/include/ptlib/msos/ptlib/svcproc.h
/usr/include/ptlib/msos/ptlib/syncpoint.h
/usr/include/ptlib/msos/ptlib/tcpsock.h
/usr/include/ptlib/msos/ptlib/textfile.h
/usr/include/ptlib/msos/ptlib/thread.h
/usr/include/ptlib/msos/ptlib/timeint.h
/usr/include/ptlib/msos/ptlib/timer.h
/usr/include/ptlib/msos/ptlib/udpsock.h
/usr/include/ptlib/msos/ptlib/video.h
/usr/include/ptlib/msos/ptlib/videoio.h
/usr/include/ptlib/msos/ptlib/vidinput_directx.h
/usr/include/ptlib/msos/ptlib_2003.dtf
/usr/include/ptlib/msos/ptlibd.dtf
/usr/include/ptlib/msos/ptlibd_2003.dtf
/usr/include/ptlib/msos/ptlibn_2005.dtf
/usr/include/ptlib/msos/unistd.h