In the pouranic age and upto the middle of the 13th century A.D of historic period , North –East India was known as Kamrupa . But after 1255 A.D Kamrupa was renamed as Kamatapura on t he transfer of its capital from Gouhati to Kamatapur , 15 miles South – west to the present city of Cooch Behar .
During the Kamrupi period (9 A.D) language entered this large area from the West i.e from Magadh and Mithila . Dr. Sunity kumar Chatterjee , the reknowned philologist opined : “It can not be defined when the Aryan speech first came to North Bengal probably from Mithila and Central South Bengal from Anga .” (O,D.B.L) Dr. Chatterjee also said _ ‘from its geographical position Assam was practically an extension of North Bengal , so far as its speech and early history was concerned (O.D.B.L) .
Abraham Griarson also voiced the same idea . He said ,’North Bengal and Assam did not get their language from Bengal properly but directly from west . Magadhi Apabhransa , in fact may be considered as spreading out east wards and south wards in three directions . To the northeast it developed into Northern Bengali and Assamese ,to the south is Oriya and between the two into Bengali .” ( linguistic survey of India )
Dr. Bani Kanta Kakati in his ,’Assamese its formation and Development ‘ said _” It would thus appear tha t there is no question o one dialect group having sprung out of another _ they are all related to one another as having emanated from one centre of radiation and yet following their line of development .” It is a fact that in ancient times there was a cultural and social inter course between Mithila and Kamrupa and so in linguistic sphere also. Click here to read the full article