The northern boundary of T39N-R4E is the east-west solid line below the "dashed" line at the top of the image; it runs through the northern part of De Soto. The western boundary is the second north-south line from the left edge of the map. The eastern boundary is the first full-length north-south line from the right edge of the map. The southern boundary is the east-west (more or less) line just above the "T 38 N" that's printed near the bottom left of the map.
The northern boundary of T38N is the southern boundary of T39N, and it also has the same eastern boundary line as T39N.
Note that Big River forms the southwestern border of these townships and this portion of the county.