2.8 Place these books on the same shelf of a bookcase. Find the probability that 4 specified books are placed in the middle.

Place the above text in English, keeping the original text's line breaks and format, and output the translation result directly.
$\begin{array}{l}\text { (Answer: } \mathrm{P}=\frac{\mathrm{P}_{4}^{4} \cdot \mathrm{P}_{4}^{4}}{\mathrm{P}_{8}^{8}} \\ =\frac{1}{70} \text { ) }\end{array}$