THE HAIR 



295 



is known also as the epitrichium (layer upon the hair). Desquamated epitrichial 

 and epidermal cells mix with the secretion of the sebaceous glands to form the 

 cheesy vernix caseosa which covers the fetal skin. Pigment granules appear soon 

 after birth in the cells of the stratum germinativum. These granules are prob- 

 ably formed in situ. Negro children are quite hght in color at birth, but within 

 six weeks their integument has reached the normal degree of pigmentation. 



The derma or corium of the integument is developed from mesenchyme, 

 perhaps from that of the dermatomes (Fig. 323) of the mesodermal segments (p. 

 292). At about the end of the third month a differentiation into the compact 



Epitrichium 

 Stratum germinativum^^ 



Epitrichium 



Intermediate layer 

 Stratum germinativum 



Corium- 





)QKaL.rtne MilV 



Fig. 299. — Sections of the integument from a 65 mm. human fetus. X 440. A, Section through 

 the integument of the neck showing a two-layered epidermis and the beginning of a third intermediate 

 layer; B, section from the integument of the chin in which three layers are well developed in the epidermis. 



corium proper and the areolar subcutaneous tissue occurs. From the corium 

 papillcB project into the stratum germinativum. 



Anomalies. — Dermoid cysts, resulting from epidermal inclusions, are not infrequent 

 along the lines of fusion of embryonic structures, e. g., branchial clefts, mid-dorsal and mid- 

 ventral body wall. 



THE HAIR 



Hairs are derived from tliickenings of the epidermis and begin to develop at 

 the end of the second month on the eyebrows, upper lip, and chin. The hair of 

 the general body integument appears at the beginning of the fourth month. 



The first evidence of a hair anlage is the elongation of a cluster of epidermal 

 cells in the inner germinal layer (Fig. iOQ A). The bases of these cells project into 

 the corium, and, above them, cells of the epidermis are arranged parallel to the 



