The inner coffins were often contained in a rectangular coffin, which was often painted to represent a 'mastaba' tomb from the earliest periods of Egyptian history.
Like most aspects of the Egyptian funerary beliefs there were reoccurring themes throughout the ages. What would originally have been a stone building came to be represented by paintings.
The inclusion of the eyes, which are very common on this type of coffin, enabled the deceased to see what was going on.