Connect Polylines
Click the Features | Edit Polylines
| Connect Polylines command or the 
button or right-click on the selection and
click Connect Polylines to connect
selected polylines and spline polylines. The polylines are connected at
the closest endpoints on each line. For the command to be available, two
or more polylines, 3D polylines or spline polylines must be selected. 3D polylines cannot be connected to polylines or spline polylines.
The new polyline or 3D polyline retains the line properties from the polyline at the bottom of the Contents window. If the object name has not been changed from the default Polyline, the object is renamed Polyline. If the object name had been altered, the custom object name from the bottom polyline is retained.