Hare-lip, or coloboma of the upper lip, is due to a failure in coalescence of the developing maxillary processes, which should unite early in fetal life to form the lip, alveolar process and roof of the mouth. This failure may involve but a trifling part of this line of normal junction or may be complete. Thus anywhere along it defects may be noted, such, for instance, as a little notch in the lip, a small opening in the hard or soft palate, or a bifid uvula. The defect in the lip alone is known as hare-lip because of its normal occurrence in the hare, and occurs on either side of the median line, absolute median fissure being extremely rare. It may occur alone or in combination with deeper fissures which involve the gum or the alveolar process alone or the entire palate. In extensive fissures of this character development is rarely symmetrical, and one side is usually not developed sufficiently to match the other. This makes operative treatment the more difficult. The more complete and extensive fissures are often complicated by excessive development of the intermaxillary bone, apparently from lack of pressure. This permits a projection of the septum, and especially of the central portion of the alveolar process, with a small part of the skin and connective tissue, which should have been blended into the lip proper. It represents the original intermaxillary bone with the portion which should have been developed downward from the nasal process of the midfrontal region. This gives a snout-like appearance to the face, and nearly always necessitates doing an operation for closure of the lip in two sittings. In [Figs. 445] and [446] will be seen wide clefts with projecting intermaxillaries, while [Fig. 447] illustrates a much more complete coloboma of the face, with complete bilateral fissures. [Figs. 448] and [449] show the double form with philtrum or snout. [Figs. 450] and [451] give the palatal conditions of irregularity and projection of the intermaxillary bone. (See [Cleft Palate].)
Fig. 445
Incomplete hare-lip.
Fig. 446
Fig. 447
Complete fissure in double hare-lip.
Complete bilateral fissures (coloboma) of face. (Guersant.)