The arrangement of muscle fibres in cleft lips.

A total of 63 laterally situated partial clefts of the lip were studied. The biopsies obtained during the first operation were evaluated histologically. With a special stain, the fibre of the orbicularis oris muscle were demonstrated and their arrangement in relation to the cleft lip was recorded. The results indicate a close relationship between type and degree of the cleft and the arrangement of the muscle bundles: In microforms like lip indentations and minor clefts of the lip the natural anatomy is almost unaltered. The muscle "flows" around the "obstacle". But the larger the cleft the more often the muscle fibres end right at the border of the cleft and insertions are often found here. In the remaining skin bridge the number of muscle fibres decreases and their arrangement deteriorates. In the extreme forms, i.e. the band of Simonart and the completely cleft lip, we must assume that most of the fibres stop at the border of the cleft as muscle no longer crosses the defect.