Layout > Working with Entities > Modifying Entities > About Merging and Dividing Entities
  
About Merging and Dividing Entities
You can use the Merge tool to join tangent lines, splines, or arcs that share an endpoint into a single entity. You can use the Divide tool to divide single lines, splines, and arcs into two or more entities.
Keep in mind the following points when merging tangent entities:
They must be of the same type.
They do not need to share a same point constraint.
The curvature of splines does not need to be the same.
When two entities belong to two nodes, the merged entity belongs to the node of the first selected entity.