  For $n\ge 6$ let $V=\{v_0,v_1,\ldots,v_{n-1}\}$,
$E_1=\{v_0v_1,\ldots,v_0v_{n-4},v_1v_{n-3},v_1v_{n-2}$, $v_1v_{n-1}\}$,
$E_2=\{v_0v_1,\ldots,v_0v_{n-4},v_1v_{n-3},v_1v_{n-2},v_2v_{n-1}\}$,
$E_3=\{v_0v_1,\ldots,v_0v_{n-4}$, $v_1v_{n-3},v_2v_{n-2},v_3v_{n-1}\}$,
$T_n^3=(V,E_1),\ T_n^{''}=(V,E_2)$ and $T_n^{'''} =(V,E_3).$ In this paper, for
$p\ge n\ge 15$ we obtain explicit formulas for $ex(p;T_n^3)$, $ex(p;T_n^{''})$
and $ex(p;T_n^{'''})$, where $ex(p;L)$ denotes the maximal number of edges in a
graph of order $p$ not containing $L$ as a subgraph.
