*sphenethmoid*

a. [ Sphenoid + ethmoid. ] (Anat.) Of or pertaining to both the sphenoidal and the ethmoidal regions of the skull, or the sphenethmoid bone; sphenethmoidal. [ 1913 Webster ]

Sphenethmoid bone (Anat.), a bone of the skull which surrounds the anterior end of the brain in many amphibia; the girdle bone. [ 1913 Webster ]