The Later Records relating to North Westmorland by John F. Curwen (1932) on British History Online.
Cumbria County History Trust has published a "Jubilee Digest" for the township of Musgrave.
Magna Britannica et Hibernia.Volume 6: Westmorland by Thomas Cox (Vicar of Bromfield, Essex) 45 pages, printed in 1731. Transcription by Sarah Reveley, Joan Fisher and Lisl Schoenwald. (Rootsweb Westmorland Listmembers) (c) 2003:
"Musgrave Great and Little, are two small Villages of no Note, but for giving a Name to the warlike Family of the Musgraves, which is Cambden's Opinion; but our more modern Antiquaries think, and as they add, with greater Probability, that the towns had their Names from the Family. For the Name of Musgrave is to be reckoned among those that are taken from Offices, and civil or military Honours, and is of the like Original as Landt-graff, Markgraff, and Burghgraffe; and 'tis probable that this Name, and Markgraffe, (now turned into our English Marquis) are much the same. Their Signification is Dux Limitaneus, which we call a Lord Warden of the Marches: 'Tis probable that this Family of Musgraves had a Seat here, because Thomas Lord Musgrave, 32 Edw. III. obtained a Charter of Free Warren in all his Demesne Lands here, with a Power to impark his Woods called Hevenings in these Towns, containing Two hundred Acres.What more is remarkable of this Family, ee above in Herkla-Castle, and Heartley Castle. The family of Musgraves, though none of them noble after the Death of the said Thomas, yet have continued almost ever since Men of Note; but these Lordships after his Death must have been some Way alienated from his Posterity, because we find Roger Lord Clifford 4th died possessed of these Manors 13 Rich. II. and left them to his Son and Heir Thomas, etc."