It is not in the documentation (therefore unsupported and subject to change). The variable $Dataset`\$ElisionThreshold$ does what you want. The attached notebook has examples.

PLEASE NOTE: $Dataset`\$ElisionThreshold$ was added in Mathematica 10.0.2.

Quick example: with the default value

In[1]:= Dataset`$ElisionThreshold
Out[1]= 64

In[2]:= ExampleData[{"Dataset", "Titanic"}]

16 lines are printed. Lowering the value to 10 reduces the number of lines to three.

In[3]:= Dataset`$ElisionThreshold = 10;

In[4]:= ExampleData[{"Dataset", "Titanic"}]

Setting a higher number prints more rows. 144 would probably work for your example. It appears to set the number of elements included in the output.