Prior to about 1895 all collars found on knitted garments would have been a traditional round (crew) neck as in the photo below.
In 1895 the polo neck collar was introduced as shown in the example below:
By 1911 the V-neck had been introduced, this could be knitted in many different ways the example below being just one:
In the 1920’s and 1930’s many new types of collar were introduced, including the following example of an open collar:
Deep round necks were also popular in the 1930’s and were found on sweaters designed for both sexes.
By the 1950’s collars had further evolved to include cowl necks an example of a short cowl neck collar (popular in the 1950’s) is shown here:
In more recent times many variations of knitted collar have been developed.