The typology of the human fetal lanugo on the thorax.

The aim of this work is the systematic study of the skin pilosity pattern on the human trunk during the prenatal period. The course of the lanugo streams and the frequency of the occurrence of the lanugo whorls on the anterior and posterior wall of the thorax are studied on the material of 309 fetuses (163 male and 146 female). The gestational age ranged from 140 to 196 days postconception. The main four whorl types (variations) on the anterior wall and three whorl types on the posterior wall are defined. It is proved that "the cross pattern" is the dominant pattern on the anterior wall (freq. 52.9%). Less frequent variations are "the cross pattern with thoracic whorls" (freq. 15.7%) and "the cross pattern with abdominal whorls" (freq. 22.9%). The rare variation is "the whorl pattern". A few subtypes can be differentiated from each variation. On the other hand, on the posterior wall "the vertebral column path" pattern is the typical pattern (freq. 69.9%). As a runner-up with frequency of 25.8% is "the single whorl pattern". "The multiwhorl pattern" is the rare variation (freq. 4.3%). A few subtypes are separated from each variation.