Reference for Chullin 249:16

רישא קמ"ל דמוח מבפנים אינו מעלה ארוכה מבחוץ

then surely it is a proper limb, and it should convey uncleanness by overshadowing? - Rab Judah the son of R'Hiyya said: This proves that the marrow within cannot restore [the flesh] outside it.

Jastrow