7 2 



HUMAN EMBRYOLOGY AND MORPHOLOGY. 



a process of epidermis. Hairs appear to have been primarily touch 

 organs and are modifications of the touch bodies found in the skin 

 of Eeptilia (Gegenbaur). These touch bodies are composed of 



corneous layer 

 , ' stratum lucidum 

 f^rete mucosum 



germinal f «^#««|I^6asa/ layer 

 lauer \ !S, r w^$M^^£m^rT?>~.nnrium 



/^corium 

 hair point 



sebaceous gland 



hair sheath 



air 



papilla 



Fig. 55. — Diagram of a Developing Hair. 



epithelial cells, having the same shape and arrangement as those 

 which form the taste buds round the circumvallate papillae of the 

 human tongue. The cells which cap the hair papilla evidently 

 represent the primary sensory cells of the touch bodies ; they are 

 situated in line, and continuous with the basal or germinal layer 

 of the skin (Fig. 55). They produce the cells of the medulla of the 

 hair which bursts through the epidermis (Fig. 55). The primary 

 function of the hairs as touch organs is seen in the vibrissae 

 round the mouths of carnivora, but the hair of man no longer 

 is subservient to the sense of touch. 



The first stage in the development of a hair is the ingrowth of 

 epidermis as a solid bud, which pushes in front of it the dermis 

 to form the papilla on which the hair grows (Fig. 55). Only the 

 two deeper of the primary layers of the epidermis are carried 

 inwards to form the hair sheath and hair root. 



The hairs produced at the fifth month are fine in texture 

 (lanugo), and by the 7 th month the whole body is covered by it. 



