The hyoid North American squirrels, Sciuridae, with remarks on associated musculatura

Abstract

THE HYOID APPARATUS OF SQUIRRELS, SCIURIDAE, CONSIST OF A BASIHYAL AND PAIRED THYROHYALS, HYPOHYALS (SOMETIMES ABSENT), CERATOHYALS (FREQUENTLY EACH OF TWO PARTS), AND STYLOHYALS. TYMPANOHYALS ARE ABSENT OR PERSIST ONLY AS SHORT PIECES OF CATILAGE. THE BASIHYAL FUSES WITH THE THYROHYALS AT AN EARLY AGE. CERATOHYALS ARE LONG, USUALLY LONGER THAN THE BASIHYAL. THE HYOID CORNUA ARE BETTER DEVELOPED THAN IN MOST OTHER RODENTS, AND THE LENGHT OF ONE HYPOHYAL ONE CERATOHYAL ONE STYLOHYAL EQUALS 4.4 TO 8.3 (AVERAGE, 6.4) PER CENT OF THE LENGTH OF THE SQUIRREL 'S BODY. TREE SQUIRRELS LACK HYPOHYALS, THYROHYALS ARE SHORT, AND THE BASIHYAL IS THICK, TRIANGULAR IN CROSS-SECTION, AND LONG. FLYING SQUIRRELS HAVE A CONSPICUOUS GENIOGLOSUS MUSCLE, A DOUBLE ANTERIOR DIGASTRIC MUSCLE, AND A STYLOGLOSSUS MUSCLE CONSISTING OF TWO ELEMENTS. TERRESTRIAL SQUIRRELS HAVE A BASIHYAL CIRCULAR IN CROSS-SELECTION, LONG THYROHYALS, AND THE HYPOHYALS PRESENT IN ALL EXCEPT EUTAMIAS. OTHERS WITH HYPOHYALS ARE CALLOSPERMOPHILUS, SERMOPHILUS, OTOSPERMOPHILUS, AND ICTIDOMYS. AMMOSPERMOHILUS HAS THE MYLOHYOID AS A DOUBLE SHEET. IN THE CHIPMUNK TAMIAS, HYPOHYALS ARE PRESENT, ABSENT IN EUTAMIAS; IN TAMIAS, CERATOHYALS ARE THINNER AND STRAIGHTER THAN IN EUTAMIAS; OTHER DIFFERENCES ARE FOUND IN THE POSITIONS OF THE GENIOHYOID, HYGLOSSUS, AND STYLOGSSUS.