Alar foramen

 The base (cranial part) of each wing of atlas is perforated by the alar foramen (it may be absent in carnivores, replaced by a alar notch) for passage of vertebral artery.

The alar foramen is absent in carnivores, replaced by an alar notch. Note that authors in Miller's book describe an alar foramen in dog, but it seems to be a mistake, the labeled anatomical structure corresponding to the transverse foramen of the atlas (according to Barone and G. Constantinescu)