Looked okay at first, some interesting info, some stuff I don't really agree with, then I found this:
http://www.petmd.com/dog/breeds/c_dg_st ... ll_terrier
.....The dog’s small size makes it incredibly agile and its heavy musculature offers it great power and strength. The wide head is spacious enough for the locking of jaw muscles.
Still looking for an address to contact them.......