In the motions of the human tongue there are recognizable some hereditary abnormalities. For the criterion to roll the right and left extremities of the tongue upwards and make a small tunnel the percentage of individuals unable to perform this motion decreases and becomes almost constant about the age of twelve years; 17% in girls and 26% in boys (Table 1).
The hereditary type of this abnormality seems to be a simple Mendelian recessive (Fig. 1 and Table 2).
