Kim's classification type IV:
Kim et al Classification
Root Apex cross-section
Narrow ribbon-shaped connection that contains pulp or pulpally derived tissue : ISTHMUS
According to Kim et al classification; there are 5 types:

Type I : Incomplete isthmus between 2 canals.
Type II : Well defined, complete isthmus between 2 canals.
Type III : Very short but complete isthmus between 2 canals.
Type IV : 3 or more canals with the complete or incomplete isthmus.
Type V : 3 or more canals without any visible connection.
Incomplete isthmus between two canals
Well defined complete isthmus between two canals
3 or more canals with complete or incomplete isthmus
3 or more canals without any visible connections