 Although the zygomatic plates ( plates of bone at the side of the skull ) are variable , their size is generally intermediate for the Akodon boliviensis group and their front margin ranges from straight to a little concave . The zygomatic notches , projections at the front of the plates , are better developed than in A. caenosus and A. sylvanus . The incisive foramina ( openings in the front part of the palate ) are long , sometimes extending between the first upper molars . Tiny posterolateral palatal pits are located at the back of the palate . The back margin of the palate is squared to rounded , with a spine in the middle ( medial process ) sometimes present . The opening behind the palate , the mesopterygoid fossa , is of intermediate width , being narrower than in A. sylvanus , A. simulator , and A. budini but broader than in A. caenosus . 
