Although these original writs were thus very numerous, the extent of the jurisdiction of each writ was very limited. For example, the famous Assize of Mort d'Ancestor could be used to recover land of which the plaintiff claimed as either the heir of his father, mother, uncle, aunt, brother, or sister, but could not however, be extended to cover the case where the land was claimed as the heir of the grandfather or cousin, and new actions were necessary to provide for such cases.

In early times the Clerks of Chancery to whom the duty of issuing these original writs fell, were permitted to issue new writs to cover new cases as they arose. Afterwards, however, for reasons explained later in this work, this right was taken from them, with the result that the common law became very rigid and failed absolutely to furnish relief in many cases where rights or wrongs undoubtedly existed.

7 Pollock and Maitland's History of English Law. Volume II, page 563. First Edition.

An attempt was made to remedy this by the provision of the Statute of Westminster II, that the Clerks in Chancery, should be authorized to issue writs in cases which could not be brought under any of the existing forms of writs but which were similar to cases covered by the existing writs. This statute was the basis for a few new forms of action (e. g., Trespass on the Case, Trover, Assumpsit, etc., which will be discussed under the subject of Common Law Pleading) but did not entirely remedy the existing conditions. For this purpose a supplemental system of jurisprudence was found necessary.8