OF THE HAIRS. 189 



structureless membrane, which appears very early, is, not im- 

 probably, closely related to the external cells of the rudiment of 

 the hair, answering to the outer hair-sheath, and formed by ;ui 

 excretion from them like the membraiue propria of the glands ; 

 as to the papilla it is hardly possible to consider it as any- 

 thing but an outgrowth of the fibrous layer of the hair-sac, 

 analogous to the papillae of the cutis in general ; though 

 the circumstance that it appears at a time when the hair-sac is 

 hardly demonstrable as a whole, and that it may always be 

 pulled out together with the rudiments of the hair and root- 

 sheath, is apparently opposed to this view. 



[The first rudiments of the downy hairs and of their sheaths, 

 are found in the human embryo at the end of the third or at the 

 beginning of the fourth month, upon the forehead and eyebrows. 

 They consist of papilliform masses of cells 0-02"' in diameter 

 (fig. 73), which are visible, even to the naked eye, as minute 

 whitish spots separated by regular intervals. They are con- 

 tinuously connected with the rete Malpighii of the epidermis 

 and are nothing more than per- Fig. 73. 



fectly solid processes of it, which &. — -r—^^^-^"""^ ~— — 



penetrate obliqu ely into the corium, ~""- x ~- y-~~^~~ J 



and here lie in the meshes of a 



delicate capillary network; these 



cells are spherical 003 — 004"' i 



in diameter, and consist of a 



clear granular substance and m 



round nuclei of 0002 — 0-003'". Nothing was to be seen of 



any dermic investment of these rudiments; in other words the 



foundation of what I have described as the proper hair-sac was 



not laid. In the fifteenth week the processes were already 



larger (0-025 — 0-03'" long, 0-013—0-02'" broad), flask-shaped, 



and surrounded by a thin structureless investment, which was 



continued into a delicate membrane lying between the cutis and 



the rete Malpighii, but united more closely with the latter. 



Besides this investment, which is, probably, only the structureless 



Fig. 73. Rudiment of the hair from the brow of a human embryo, sixteen weeks 

 old, x 350 : a, horny layer of the epidermis ; b, its mucous layer ; i, structureless 

 membrane surrounding the rudiment of the hair and continued between the mucous 

 layer and the corium ; m, roundish, partly elongated cells, which especially compose 

 the rudiment of the hair. 



