DEVELOPMENT OF LEPUS 



235 



from the follicle and grows freely out. The centre of the 

 hairshaft is composed of the medulla ; surrounding this is the 

 cortex, and round this again is the cuticle. The outer wall 

 of the follicle forms a sheath round the base of the hair, and 

 the following layers can be made out in it. In contact with 

 the cuticle of the hair is the cuticle of the sheath, and next 

 outside that are Huxley's layer, Henle's layer, and the main 



Fig. 112. — Sections through the skin of mammalian embryos showing stages 

 in the development of the hairs. 



A, early stage showing the ectodermal inpushing (ei) i nd the concentra- 

 tion of the mesoderm to form a papilla (mp) ; B, the ectoderm forms a 

 follicle (/) inside which the hair (h) is developing ; C, late stage after the 

 hair has erupted from the surface, apm, arrector pili muscle ; sg, sebaceous 

 gland. 



epidermal layer of the sheath. Surrounding this again is the 

 dermal sheath of the follicle. The epidermis of the wall of the 

 follicle gives rise to little pouches which become the sebaceous 

 glands. Some mesenchyme cells outside the follicle become 

 differentiated into smooth muscle-fibres ; they gain attach- 

 ment to the wall of the follicle and become the arrector muscles 

 of the hair. 



