The latter are seen on the pole in the foreground and upon the third pole in. These wooden boxes contained terminals for joining open wire circuits to paired, enclosed cable. This practice was popular for making connections to nearby telegraph offices (within railroad depots) and for short stretches where there was not enough physical clearance for open wire, such as for runs beneath bridges.

Note the individual sections of wire leading to the box you see. Ordinarily wire tapped from such openwire deadends was ran along the underside of crossarms through white eyelet insulators...and then to the box.